Repository: RustCrypto/block-modes (language: rust)

Issue:
Support for CTS?
Some standards like Kerberos like to use block modes that are really rare and uncommon. One of these is CTS which is referenced https://www.rfc-editor.org/rfc/rfc8009#section-1 and [SP800-38+](https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38a-add.pdf) in section 4.

However, almost nothing supports this. It would be great if it could be added to this this crate, since I'm certainly not a cryptographer and I am not confident to implement it myself. :) 


Discussion / hints:
I ended up digging into this pretty deeply to try to understand the problem space. I'm not sure it's possible in this crate?

The issue is that in CTS mode, the input isn't a multiple of block size. This ends up throwing off the interfaces of this crate which assume blocks will have been pre-padded if required. 

The closest I could find that suits the behaviour here with CTS is actually https://docs.rs/aes-gcm/0.10.3/aes_gcm/type.Aes128Gcm.html since that user interface doesn't rely on a blocksize that is fixed. But of course, these traits are related to the AEAD traits which CTS doesn't satisfy. So awkwardly, this would probably actually mean for the CTS modes that a new trait for non-authenticated but also non-padded types are needed. 

So perhaps that becomes too much to ask to add since that's a lot of additions (the traits for CipherTextStealing in addition to CBC-CS1, 2 and 3.) 
CS2 and CS3 can be implemented generically over block modes (e.g. it will be useful for [Belt modes](https://github.com/RustCrypto/block-modes/pull/45)). IIRC CS1 can be implemented only for CBC. We do not have suitable traits for them right now, but we can start with inherent methods.

I have a draft implementation, but it's not finished yet.
@newpavlov hey. Could you share your draft implementation? Maybe I can finish it. Need it so much.

Fix patch:
diff --git a/.github/workflows/cts.yaml b/.github/workflows/cts.yaml
new file mode 100644
index 0000000..88eda00
--- /dev/null
+++ b/.github/workflows/cts.yaml
@@ -0,0 +1,60 @@
+name: cts
+
+on:
+  pull_request:
+    paths:
+      - "cts/**"
+      - "Cargo.*"
+  push:
+    branches: master
+
+defaults:
+  run:
+    working-directory: cts
+
+env:
+  CARGO_INCREMENTAL: 0
+  RUSTFLAGS: "-Dwarnings"
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        rust:
+          - 1.81.0 # MSRV
+          - stable
+        target:
+          - thumbv7em-none-eabi
+          - wasm32-unknown-unknown
+    steps:
+      - uses: actions/checkout@v4
+      - uses: RustCrypto/actions/cargo-cache@master
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ matrix.rust }}
+          targets: ${{ matrix.target }}
+      - run: cargo build --no-default-features --release --target ${{ matrix.target }}
+
+  minimal-versions:
+    # disabled until belt-block gets published
+    if: false
+    uses: RustCrypto/actions/.github/workflows/minimal-versions.yml@master
+    with:
+        working-directory: ${{ github.workflow }}
+
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        rust:
+          - 1.81.0 # MSRV
+          - stable
+    steps:
+      - uses: actions/checkout@v4
+      - uses: RustCrypto/actions/cargo-cache@master
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ matrix.rust }}
+      - run: cargo test
+      - run: cargo test --all-features
diff --git a/Cargo.lock b/Cargo.lock
index d899f9d..f445a21 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,17 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "aes"
+version = "0.8.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b169f7a6d4742236a0a00c541b845991d0ac43e546831af1249753ab4c3aa3a0"
+dependencies = [
+ "cfg-if",
+ "cipher 0.4.4",
+ "cpufeatures",
+]
+
 [[package]]
 name = "aes"
 version = "0.9.0-pre.2"
@@ -9,25 +20,34 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e7856582c758ade85d71daf27ec6bcea6c1c73913692b07b8dffea2dc03531c9"
 dependencies = [
  "cfg-if",
- "cipher",
+ "cipher 0.5.0-pre.7",
  "cpufeatures",
 ]
 
+[[package]]
+name = "belt-block"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9aa1eef3994e2ccd304a78fe3fea4a73e5792007f85f09b79bb82143ca5f82b"
+dependencies = [
+ "cipher 0.4.4",
+]
+
 [[package]]
 name = "belt-block"
 version = "0.2.0-pre.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6df0a14d60362d7b6041d3fe85dfd787ced16c4928f93d72152142c67d01d0bc"
 dependencies = [
- "cipher",
+ "cipher 0.5.0-pre.7",
 ]
 
 [[package]]
 name = "belt-ctr"
 version = "0.2.0-pre"
 dependencies = [
- "belt-block",
- "cipher",
+ "belt-block 0.2.0-pre.2",
+ "cipher 0.5.0-pre.7",
  "hex-literal",
 ]
 
@@ -50,8 +70,8 @@ dependencies = [
 name = "cbc"
 version = "0.2.0-pre.2"
 dependencies = [
- "aes",
- "cipher",
+ "aes 0.9.0-pre.2",
+ "cipher 0.5.0-pre.7",
  "hex-literal",
 ]
 
@@ -59,9 +79,9 @@ dependencies = [
 name = "cfb-mode"
 version = "0.9.0-pre"
 dependencies = [
- "aes",
- "belt-block",
- "cipher",
+ "aes 0.9.0-pre.2",
+ "belt-block 0.2.0-pre.2",
+ "cipher 0.5.0-pre.7",
  "hex-literal",
 ]
 
@@ -69,8 +89,8 @@ dependencies = [
 name = "cfb8"
 version = "0.9.0-pre"
 dependencies = [
- "aes",
- "cipher",
+ "aes 0.9.0-pre.2",
+ "cipher 0.5.0-pre.7",
  "hex-literal",
 ]
 
@@ -80,6 +100,17 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
+[[package]]
+name = "cipher"
+version = "0.4.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "773f3b9af64447d2ce9850330c473515014aa235e6a783b02db81ff39e4a3dad"
+dependencies = [
+ "blobby",
+ "crypto-common 0.1.6",
+ "inout 0.1.3",
+]
+
 [[package]]
 name = "cipher"
 version = "0.5.0-pre.7"
@@ -87,20 +118,30 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5b1425e6ce000f05a73096556cabcfb6a10a3ffe3bb4d75416ca8f00819c0b6a"
 dependencies = [
  "blobby",
- "crypto-common",
- "inout",
+ "crypto-common 0.2.0-rc.1",
+ "inout 0.2.0-rc.0",
  "zeroize",
 ]
 
 [[package]]
 name = "cpufeatures"
-version = "0.2.13"
+version = "0.2.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "51e852e6dc9a5bed1fae92dd2375037bf2b768725bf3be87811edee3249d09ad"
+checksum = "608697df725056feaccfa42cffdaeeec3fccc4ffc38358ecd19b243e716a78e0"
 dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "crypto-common"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1bfb12502f3fc46cca1bb51ac28df9d618d813cdc3d2f25b9fe775a34af26bb3"
+dependencies = [
+ "generic-array",
+ "typenum",
+]
+
 [[package]]
 name = "crypto-common"
 version = "0.2.0-rc.1"
@@ -116,13 +157,33 @@ dependencies = [
 name = "ctr"
 version = "0.10.0-pre.2"
 dependencies = [
- "aes",
- "cipher",
+ "aes 0.9.0-pre.2",
+ "cipher 0.5.0-pre.7",
  "hex-literal",
  "kuznyechik",
  "magma",
 ]
 
+[[package]]
+name = "cts"
+version = "0.6.0"
+dependencies = [
+ "aes 0.8.4",
+ "belt-block 0.1.2",
+ "cipher 0.4.4",
+ "hex-literal",
+]
+
+[[package]]
+name = "generic-array"
+version = "0.14.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85649ca51fd72272d7821adaf274ad91c288277713d9c18820d8499a7ff69e9a"
+dependencies = [
+ "typenum",
+ "version_check",
+]
+
 [[package]]
 name = "getrandom"
 version = "0.2.15"
@@ -153,11 +214,20 @@ dependencies = [
 name = "ige"
 version = "0.2.0-pre"
 dependencies = [
- "aes",
- "cipher",
+ "aes 0.9.0-pre.2",
+ "cipher 0.5.0-pre.7",
  "hex-literal",
 ]
 
+[[package]]
+name = "inout"
+version = "0.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a0c10553d664a4d0bcff9f4215d0aac67a639cc68ef660840afe309b807bc9f5"
+dependencies = [
+ "generic-array",
+]
+
 [[package]]
 name = "inout"
 version = "0.2.0-rc.0"
@@ -175,14 +245,14 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bd136ca56393426d0aeca01643adef06b1f30d667fdebf31f7cf11724cbd9051"
 dependencies = [
  "cfg-if",
- "cipher",
+ "cipher 0.5.0-pre.7",
 ]
 
 [[package]]
 name = "libc"
-version = "0.2.155"
+version = "0.2.161"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "97b3888a4aecf77e811145cadf6eef5901f4782c53886191b2f693f24761847c"
+checksum = "8e9489c2807c139ffd9c1794f4af0ebe86a828db53ecdc7fea2111d0fed085d1"
 
 [[package]]
 name = "magma"
@@ -190,15 +260,15 @@ version = "0.10.0-pre.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b9fd466f879a2c01f141f168c4e045a26dca5a60aef79efa8bb96e9c701bb8ea"
 dependencies = [
- "cipher",
+ "cipher 0.5.0-pre.7",
 ]
 
 [[package]]
 name = "ofb"
 version = "0.7.0-pre"
 dependencies = [
- "aes",
- "cipher",
+ "aes 0.9.0-pre.2",
+ "cipher 0.5.0-pre.7",
  "hex-literal",
 ]
 
@@ -206,8 +276,8 @@ dependencies = [
 name = "pcbc"
 version = "0.2.0-pre"
 dependencies = [
- "aes",
- "cipher",
+ "aes 0.9.0-pre.2",
+ "cipher 0.5.0-pre.7",
  "hex-literal",
 ]
 
@@ -226,6 +296,12 @@ version = "1.17.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "42ff0bf0c66b8238c6f3b578df37d0b7848e55df8577b3f74f92a69acceeb825"
 
+[[package]]
+name = "version_check"
+version = "0.9.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0b928f33d975fc6ad9f86c8f283853ad26bdd5b10b7f1542aa2fa15e2289105a"
+
 [[package]]
 name = "wasi"
 version = "0.11.0+wasi-snapshot-preview1"
diff --git a/Cargo.toml b/Cargo.toml
index 4db8e0a..adffbe5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [workspace]
 resolver = "2"
-members = ["belt-ctr", "cbc", "cfb8", "cfb-mode", "ctr", "ige", "ofb", "pcbc"]
+members = ["belt-ctr", "cbc", "cts", "cfb8", "cfb-mode", "ctr", "ige", "ofb", "pcbc"]
 
 [profile.dev]
 opt-level = 2
diff --git a/README.md b/README.md
index c660220..2144bf5 100644
--- a/README.md
+++ b/README.md
@@ -26,6 +26,7 @@ less error-prone than manual integrity verification.
 | [8-bit Cipher Feedback][CFB-8] | [`cfb8`] | [![crates.io](https://img.shields.io/crates/v/cfb8.svg)](https://crates.io/crates/cfb8) | [![Documentation](https://docs.rs/cfb8/badge.svg)](https://docs.rs/cfb8) |  ![MSRV 1.56][msrv-1.56] |
 | [Full-block Cipher Feedback][CFB] | [`cfb-mode`] | [![crates.io](https://img.shields.io/crates/v/cfb-mode.svg)](https://crates.io/crates/cfb-mode) | [![Documentation](https://docs.rs/cfb-mode/badge.svg)](https://docs.rs/cfb-mode) |  ![MSRV 1.56][msrv-1.56] |
 | [Counter][CTR] | [`ctr`] | [![crates.io](https://img.shields.io/crates/v/ctr.svg)](https://crates.io/crates/ctr) | [![Documentation](https://docs.rs/ctr/badge.svg)](https://docs.rs/ctr) |  ![MSRV 1.56][msrv-1.56] |
+| [Ciphertext stealing][CTS] | [`cts`] | [![crates.io](https://img.shields.io/crates/v/cts.svg)](https://crates.io/crates/cts) | [![Documentation](https://docs.rs/cts/badge.svg)](https://docs.rs/cts) |  ![MSRV 1.81][msrv-1.81] |
 | [GOST R 34.13-2015] | [`gost-modes`] | [![crates.io](https://img.shields.io/crates/v/gost-modes.svg)](https://crates.io/crates/gost-modes) | [![Documentation](https://docs.rs/gost-modes/badge.svg)](https://docs.rs/gost-modes) | ![MSRV 1.56][msrv-1.56] |
 | [Infinite Garble Extension][IGE] | [`ige`] | [![crates.io](https://img.shields.io/crates/v/ige.svg)](https://crates.io/crates/ige) | [![Documentation](https://docs.rs/ige/badge.svg)](https://docs.rs/ige) |  ![MSRV 1.56][msrv-1.56] |
 | [Output Feedback][OFB] | [`ofb`] | [![crates.io](https://img.shields.io/crates/v/ofb.svg)](https://crates.io/crates/ofb) | [![Documentation](https://docs.rs/ofb/badge.svg)](https://docs.rs/ofb) |  ![MSRV 1.56][msrv-1.56] |
@@ -60,6 +61,7 @@ Unless you explicitly state otherwise, any contribution intentionally submitted
 [aead-link]: https://github.com/RustCrypto/AEADs
 [msrv-1.56]: https://img.shields.io/badge/rustc-1.56.0+-blue.svg
 [msrv-1.57]: https://img.shields.io/badge/rustc-1.57.0+-blue.svg
+[msrv-1.81]: https://img.shields.io/badge/rustc-1.81.0+-blue.svg
 
 [//]: # (crates)
 
@@ -68,6 +70,7 @@ Unless you explicitly state otherwise, any contribution intentionally submitted
 [`cfb8`]: ./cfb8
 [`cfb-mode`]: ./cfb-mode
 [`ctr`]: ./ctr
+[`cts`]: ./cts
 [`gost-modes`]: ./gost-modes
 [`ige`]: ./ige
 [`ofb`]: ./ofb
@@ -81,6 +84,7 @@ Unless you explicitly state otherwise, any contribution intentionally submitted
 [CFB-8]: https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#CFB-1,_CFB-8,_CFB-64,_CFB-128,_etc.
 [CFB]: https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Full-block_CFB
 [CTR]: https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Counter_(CTR)
+[CTS]: https://en.wikipedia.org/wiki/Ciphertext_stealing
 [GOST R 34.13-2015]: https://tc26.ru/standard/gost/GOST_R_3413-2015.pdf
 [IGE]: https://www.links.org/files/openssl-ige.pdf
 [OFB]: https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Output_feedback_(OFB)
diff --git a/cts/CHANGELOG.md b/cts/CHANGELOG.md
new file mode 100644
index 0000000..5aa9b87
--- /dev/null
+++ b/cts/CHANGELOG.md
@@ -0,0 +1,11 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## 0.6.0 (2024-11-01)
+- Initial release ([#70])
+
+[#70]: https://github.com/RustCrypto/block-modes/pull/70
\ No newline at end of file
diff --git a/cts/Cargo.toml b/cts/Cargo.toml
new file mode 100644
index 0000000..9c5a2a0
--- /dev/null
+++ b/cts/Cargo.toml
@@ -0,0 +1,26 @@
+[package]
+name = "cts"
+version = "0.6.0"
+description = "Generic implementation of the ciphertext stealing block modes of operation"
+authors = ["RustCrypto Developers"]
+license = "MIT OR Apache-2.0"
+edition = "2021"
+rust-version = "1.81"
+readme = "README.md"
+documentation = "https://docs.rs/cts"
+repository = "https://github.com/RustCrypto/block-modes"
+keywords = ["crypto", "block-mode", "ciphers"]
+categories = ["cryptography", "no-std"]
+
+[dependencies]
+cipher = "0.4.2"
+
+[dev-dependencies]
+cipher = { version = "0.4.2", features = ["dev"] }
+hex-literal = "0.4"
+aes = "0.8"
+belt-block = "0.1"
+
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
diff --git a/cts/LICENSE-APACHE b/cts/LICENSE-APACHE
new file mode 100644
index 0000000..78173fa
--- /dev/null
+++ b/cts/LICENSE-APACHE
@@ -0,0 +1,201 @@
+                              Apache License
+                        Version 2.0, January 2004
+                     http://www.apache.org/licenses/
+
+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+1. Definitions.
+
+   "License" shall mean the terms and conditions for use, reproduction,
+   and distribution as defined by Sections 1 through 9 of this document.
+
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+
+   "Legal Entity" shall mean the union of the acting entity and all
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+   outstanding shares, or (iii) beneficial ownership of such entity.
+
+   "You" (or "Your") shall mean an individual or Legal Entity
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+   "Source" form shall mean the preferred form for making modifications,
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+   You may add Your own copyright statement to Your modifications and
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+   the conditions stated in this License.
+
+5. Submission of Contributions. Unless You explicitly state otherwise,
+   any Contribution intentionally submitted for inclusion in the Work
+   by You to the Licensor shall be under the terms and conditions of
+   this License, without any additional terms or conditions.
+   Notwithstanding the above, nothing herein shall supersede or modify
+   the terms of any separate license agreement you may have executed
+   with Licensor regarding such Contributions.
+
+6. Trademarks. This License does not grant permission to use the trade
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+   origin of the Work and reproducing the content of the NOTICE file.
+
+7. Disclaimer of Warranty. Unless required by applicable law or
+   agreed to in writing, Licensor provides the Work (and each
+   Contributor provides its Contributions) on an "AS IS" BASIS,
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+8. Limitation of Liability. In no event and under no legal theory,
+   whether in tort (including negligence), contract, or otherwise,
+   unless required by applicable law (such as deliberate and grossly
+   negligent acts) or agreed to in writing, shall any Contributor be
+   liable to You for damages, including any direct, indirect, special,
+   incidental, or consequential damages of any character arising as a
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+   or other liability obligations and/or rights consistent with this
+   License. However, in accepting such obligations, You may act only
+   on Your own behalf and on Your sole responsibility, not on behalf
+   of any other Contributor, and only if You agree to indemnify,
+   defend, and hold each Contributor harmless for any liability
+   incurred by, or claims asserted against, such Contributor by reason
+   of your accepting any such warranty or additional liability.
+
+END OF TERMS AND CONDITIONS
+
+APPENDIX: How to apply the Apache License to your work.
+
+   To apply the Apache License to your work, attach the following
+   boilerplate notice, with the fields enclosed by brackets "[]"
+   replaced with your own identifying information. (Don't include
+   the brackets!)  The text should be enclosed in the appropriate
+   comment syntax for the file format. We also recommend that a
+   file or class name and description of purpose be included on the
+   same "printed page" as the copyright notice for easier
+   identification within third-party archives.
+
+Copyright [yyyy] [name of copyright owner]
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
diff --git a/cts/LICENSE-MIT b/cts/LICENSE-MIT
new file mode 100644
index 0000000..e92e140
--- /dev/null
+++ b/cts/LICENSE-MIT
@@ -0,0 +1,26 @@
+Copyright (c) 2024 RustCrypto Developers
+Copyright (c) 2024 Artyom Pavlov
+
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
+documentation files (the "Software"), to deal in the
+Software without restriction, including without
+limitation the rights to use, copy, modify, merge,
+publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software
+is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice
+shall be included in all copies or substantial portions
+of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
diff --git a/cts/README.md b/cts/README.md
new file mode 100644
index 0000000..8a33ad7
--- /dev/null
+++ b/cts/README.md
@@ -0,0 +1,106 @@
+# RustCrypto: CTS
+
+[![crate][crate-image]][crate-link]
+[![Docs][docs-image]][docs-link]
+![Apache2/MIT licensed][license-image]
+![Rust Version][rustc-image]
+[![Project Chat][chat-image]][chat-link]
+[![Build Status][build-image]][build-link]
+
+Generic implementation of the [ciphertext stealing] block cipher modes of operation.
+
+## Example
+```rust
+use aes::Aes128;
+use cts::{Decrypt, Encrypt, KeyIvInit};
+use hex_literal::hex;
+
+let key = [0x42; 16];
+let iv = [0x24; 16];
+
+// Message must be bigger than block size (16 bytes for AES-128)
+let msg = b"Lorem ipsum dolor sit amet";
+let mut buf = [0u8; 26];
+
+let enc_mode = cts::CbcCs3Enc::<Aes128>::new(&key.into(), &iv.into());
+enc_mode.encrypt_b2b(msg, &mut buf).unwrap();
+assert_eq!(buf, hex!("68ec97f172e322fdd38e74fca65cee52658ae2124beb5e4e5315"));
+
+let dec_mode = cts::CbcCs3Dec::<Aes128>::new(&key.into(), &iv.into());
+dec_mode.decrypt(&mut buf).unwrap();
+assert_eq!(&buf, msg);
+```
+
+If you wan to encrypt many messages with one key, you can use a block cipher reference
+to create CTS modes:
+```rust
+use aes::Aes128;
+use cts::{
+    cipher::{InnerIvInit, KeyInit},
+    Encrypt,
+};
+use hex_literal::hex;
+
+let key = [0x42; 16];
+let cipher = Aes128::new(&key.into());
+
+let iv1 = [0x24; 16];
+let msg1 = b"Lorem ipsum dolor sit amet";
+let mut buf1 = [0u8; 26];
+
+let iv2 = [0x25; 16];
+let msg2 = b"Lorem ipsum dolor sit";
+let mut buf2 = [0u8; 21];
+
+let enc_mode = cts::CbcCs3Enc::inner_iv_init(&cipher, &iv1.into());
+enc_mode.encrypt_b2b(msg1, &mut buf1).unwrap();
+assert_eq!(buf1, hex!("68ec97f172e322fdd38e74fca65cee52658ae2124beb5e4e5315"));
+
+let enc_mode = cts::CbcCs3Enc::inner_iv_init(&cipher, &iv2.into());
+enc_mode.encrypt_b2b(msg2, &mut buf2).unwrap();
+assert_eq!(buf2, hex!("69ebd2059e69c6e416a67351982267a26bf5672934"));
+```
+
+## Minimum Supported Rust Version
+
+Rust **1.57** or higher.
+
+Minimum supported Rust version can be changed in the future, but it will be
+done with a minor version bump.
+
+## SemVer Policy
+
+- All on-by-default features of this library are covered by SemVer
+- MSRV is considered exempt from SemVer as noted above
+
+## License
+
+Licensed under either of:
+
+ * [Apache License, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0)
+ * [MIT license](http://opensource.org/licenses/MIT)
+
+at your option.
+
+### Contribution
+
+Unless you explicitly state otherwise, any contribution intentionally submitted
+for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
+dual licensed as above, without any additional terms or conditions.
+
+[//]: # (badges)
+
+[crate-image]: https://img.shields.io/crates/v/cts.svg
+[crate-link]: https://crates.io/crates/cts
+[docs-image]: https://docs.rs/cts/badge.svg
+[docs-link]: https://docs.rs/cts/
+[license-image]: https://img.shields.io/badge/license-Apache2.0/MIT-blue.svg
+[rustc-image]: https://img.shields.io/badge/rustc-1.56+-blue.svg
+[chat-image]: https://img.shields.io/badge/zulip-join_chat-blue.svg
+[chat-link]: https://rustcrypto.zulipchat.com/#narrow/stream/308460-block-modes
+[build-image]: https://github.com/RustCrypto/block-modes/workflows/cts/badge.svg?branch=master&event=push
+[build-link]: https://github.com/RustCrypto/block-modes/actions?query=workflow%3Acts+branch%3Amaster
+
+[//]: # (general links)
+
+[ciphertext stealing]: https://en.wikipedia.org/wiki/Ciphertext_stealing
diff --git a/cts/src/cbc_cs1_dec.rs b/cts/src/cbc_cs1_dec.rs
new file mode 100644
index 0000000..abbf32e
--- /dev/null
+++ b/cts/src/cbc_cs1_dec.rs
@@ -0,0 +1,88 @@
+use crate::{cbc_dec, xor, Decrypt, Error};
+use cipher::{
+    crypto_common::InnerUser, generic_array::GenericArray, inout::InOutBuf, typenum::Unsigned,
+    ArrayLength, Block, BlockBackend, BlockClosure, BlockDecrypt, BlockSizeUser, InnerIvInit,
+    IvSizeUser,
+};
+
+/// The CBC-CS-1 ciphertext stealing mode decryptor.
+#[derive(Clone)]
+pub struct CbcCs1Dec<C: BlockDecrypt> {
+    cipher: C,
+    iv: Block<C>,
+}
+
+impl<C: BlockDecrypt> InnerUser for CbcCs1Dec<C> {
+    type Inner = C;
+}
+
+impl<C: BlockDecrypt> IvSizeUser for CbcCs1Dec<C> {
+    type IvSize = C::BlockSize;
+}
+
+impl<C: BlockDecrypt> InnerIvInit for CbcCs1Dec<C> {
+    fn inner_iv_init(cipher: Self::Inner, iv: &cipher::Iv<Self>) -> Self {
+        Self {
+            cipher,
+            iv: iv.clone(),
+        }
+    }
+}
+
+impl<C: BlockDecrypt> Decrypt for CbcCs1Dec<C> {
+    fn decrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error> {
+        if buf.len() < C::BlockSize::USIZE {
+            return Err(Error);
+        }
+        let Self { cipher, iv } = self;
+        cipher.decrypt_with_backend(Closure { iv, buf });
+        Ok(())
+    }
+}
+
+struct Closure<'a, BS: ArrayLength<u8>> {
+    iv: GenericArray<u8, BS>,
+    buf: InOutBuf<'a, 'a, u8>,
+}
+
+impl<BS: ArrayLength<u8>> BlockSizeUser for Closure<'_, BS> {
+    type BlockSize = BS;
+}
+
+impl<BS: ArrayLength<u8>> BlockClosure for Closure<'_, BS> {
+    fn call<B: BlockBackend<BlockSize = BS>>(self, cipher: &mut B) {
+        let Self { mut iv, mut buf } = self;
+
+        let (mut blocks, tail) = buf.reborrow().into_chunks();
+
+        if !tail.is_empty() {
+            let mid = blocks.len() - 1;
+            blocks = blocks.split_at(mid).0;
+        };
+
+        cbc_dec(cipher, &mut iv, blocks);
+
+        if tail.is_empty() {
+            return;
+        }
+
+        let tail_len = tail.len();
+        let bs = B::BlockSize::USIZE;
+        let mid = buf.len() - (bs + tail_len);
+        let mut rem = buf.split_at(mid).1;
+
+        let n = rem.len() - bs;
+        let mut block1 = Block::<B>::clone_from_slice(&rem.get_in()[..bs]);
+        let mut block2 = Block::<B>::clone_from_slice(&rem.get_in()[n..]);
+
+        cipher.proc_block_inplace(&mut block2);
+        block1[n..].copy_from_slice(&block2[n..]);
+        xor(&mut block2, &block1);
+
+        cipher.proc_block_inplace(&mut block1);
+        xor(&mut block1, &iv);
+
+        rem.get_out()[..bs].copy_from_slice(&block1);
+        rem.get_out()[bs..].copy_from_slice(&block2[..n]);
+    }
+}
diff --git a/cts/src/cbc_cs1_enc.rs b/cts/src/cbc_cs1_enc.rs
new file mode 100644
index 0000000..9b2652c
--- /dev/null
+++ b/cts/src/cbc_cs1_enc.rs
@@ -0,0 +1,71 @@
+use crate::{cbc_enc, xor, Encrypt, Error};
+use cipher::{
+    crypto_common::InnerUser, generic_array::GenericArray, inout::InOutBuf, typenum::Unsigned,
+    ArrayLength, Block, BlockBackend, BlockClosure, BlockEncrypt, BlockSizeUser, InnerIvInit,
+    IvSizeUser,
+};
+
+/// The CBC-CS-1 ciphertext stealing mode encryptor.
+#[derive(Clone)]
+pub struct CbcCs1Enc<C: BlockEncrypt> {
+    cipher: C,
+    iv: Block<C>,
+}
+
+impl<C: BlockEncrypt> InnerUser for CbcCs1Enc<C> {
+    type Inner = C;
+}
+
+impl<C: BlockEncrypt> IvSizeUser for CbcCs1Enc<C> {
+    type IvSize = C::BlockSize;
+}
+
+impl<C: BlockEncrypt> InnerIvInit for CbcCs1Enc<C> {
+    fn inner_iv_init(cipher: Self::Inner, iv: &cipher::Iv<Self>) -> Self {
+        Self {
+            cipher,
+            iv: iv.clone(),
+        }
+    }
+}
+
+impl<C: BlockEncrypt> Encrypt for CbcCs1Enc<C> {
+    fn encrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error> {
+        if buf.len() < C::BlockSize::USIZE {
+            return Err(Error);
+        }
+        let Self { cipher, iv } = self;
+        cipher.encrypt_with_backend(Closure { iv, buf });
+        Ok(())
+    }
+}
+
+struct Closure<'a, BS: ArrayLength<u8>> {
+    iv: GenericArray<u8, BS>,
+    buf: InOutBuf<'a, 'a, u8>,
+}
+
+impl<BS: ArrayLength<u8>> BlockSizeUser for Closure<'_, BS> {
+    type BlockSize = BS;
+}
+
+impl<BS: ArrayLength<u8>> BlockClosure for Closure<'_, BS> {
+    fn call<B: BlockBackend<BlockSize = BS>>(self, cipher: &mut B) {
+        let Self { mut iv, mut buf } = self;
+        let (blocks, tail) = buf.reborrow().into_chunks();
+
+        cbc_enc(cipher, &mut iv, blocks);
+
+        if tail.is_empty() {
+            return;
+        }
+
+        let mut block = Block::<B>::default();
+        block[..tail.len()].copy_from_slice(tail.get_in());
+        xor(&mut block, &iv);
+        cipher.proc_block_inplace(&mut block);
+
+        let pos = buf.len() - B::BlockSize::USIZE;
+        buf.get_out()[pos..].copy_from_slice(&block);
+    }
+}
diff --git a/cts/src/cbc_cs2_dec.rs b/cts/src/cbc_cs2_dec.rs
new file mode 100644
index 0000000..53063c1
--- /dev/null
+++ b/cts/src/cbc_cs2_dec.rs
@@ -0,0 +1,90 @@
+use crate::{cbc_dec, xor, Decrypt, Error};
+use cipher::{
+    crypto_common::InnerUser, generic_array::GenericArray, inout::InOutBuf, typenum::Unsigned,
+    ArrayLength, Block, BlockBackend, BlockClosure, BlockDecrypt, BlockSizeUser, InnerIvInit,
+    IvSizeUser,
+};
+
+/// The CBC-CS-2 ciphertext stealing mode decryptor.
+#[derive(Clone)]
+pub struct CbcCs2Dec<C: BlockDecrypt> {
+    cipher: C,
+    iv: Block<C>,
+}
+
+impl<C: BlockDecrypt> InnerUser for CbcCs2Dec<C> {
+    type Inner = C;
+}
+
+impl<C: BlockDecrypt> IvSizeUser for CbcCs2Dec<C> {
+    type IvSize = C::BlockSize;
+}
+
+impl<C: BlockDecrypt> InnerIvInit for CbcCs2Dec<C> {
+    fn inner_iv_init(cipher: Self::Inner, iv: &cipher::Iv<Self>) -> Self {
+        Self {
+            cipher,
+            iv: iv.clone(),
+        }
+    }
+}
+
+impl<C: BlockDecrypt> Decrypt for CbcCs2Dec<C> {
+    fn decrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error> {
+        if buf.len() < C::BlockSize::USIZE {
+            return Err(Error);
+        }
+        let Self { cipher, iv } = self;
+        cipher.decrypt_with_backend(Closure { iv, buf });
+        Ok(())
+    }
+}
+
+struct Closure<'a, BS: ArrayLength<u8>> {
+    iv: GenericArray<u8, BS>,
+    buf: InOutBuf<'a, 'a, u8>,
+}
+
+impl<BS: ArrayLength<u8>> BlockSizeUser for Closure<'_, BS> {
+    type BlockSize = BS;
+}
+
+impl<BS: ArrayLength<u8>> BlockClosure for Closure<'_, BS> {
+    fn call<B: BlockBackend<BlockSize = BS>>(self, cipher: &mut B) {
+        let Self { mut iv, mut buf } = self;
+
+        let (mut blocks, tail) = buf.reborrow().into_chunks();
+
+        if !tail.is_empty() {
+            let mid = blocks.len() - 1;
+            blocks = blocks.split_at(mid).0;
+        };
+
+        cbc_dec(cipher, &mut iv, blocks);
+
+        if tail.is_empty() {
+            return;
+        }
+
+        let tail_len = tail.len();
+        let bs = B::BlockSize::USIZE;
+        let mid = buf.len() - (bs + tail_len);
+        let mut rem = buf.split_at(mid).1;
+
+        let n = rem.len() - bs;
+        let mut block1 = Block::<B>::clone_from_slice(&rem.get_in()[..bs]);
+        cipher.proc_block_inplace(&mut block1);
+
+        let mut block2 = Block::<B>::default();
+        block2[..n].copy_from_slice(&rem.get_in()[bs..]);
+        block2[n..].copy_from_slice(&block1[n..]);
+
+        xor(&mut block1, &block2);
+
+        cipher.proc_block_inplace(&mut block2);
+        xor(&mut block2, &iv);
+
+        rem.get_out()[..bs].copy_from_slice(&block2);
+        rem.get_out()[bs..].copy_from_slice(&block1[..n]);
+    }
+}
diff --git a/cts/src/cbc_cs2_enc.rs b/cts/src/cbc_cs2_enc.rs
new file mode 100644
index 0000000..2ebedfb
--- /dev/null
+++ b/cts/src/cbc_cs2_enc.rs
@@ -0,0 +1,72 @@
+use crate::{cbc_enc, xor, Encrypt, Error};
+use cipher::{
+    crypto_common::InnerUser, generic_array::GenericArray, inout::InOutBuf, typenum::Unsigned,
+    ArrayLength, Block, BlockBackend, BlockClosure, BlockEncrypt, BlockSizeUser, InnerIvInit,
+    IvSizeUser,
+};
+
+/// The CBC-CS-2 ciphertext stealing mode encryptor.
+#[derive(Clone)]
+pub struct CbcCs2Enc<C: BlockEncrypt> {
+    cipher: C,
+    iv: Block<C>,
+}
+
+impl<C: BlockEncrypt> InnerUser for CbcCs2Enc<C> {
+    type Inner = C;
+}
+
+impl<C: BlockEncrypt> IvSizeUser for CbcCs2Enc<C> {
+    type IvSize = C::BlockSize;
+}
+
+impl<C: BlockEncrypt> InnerIvInit for CbcCs2Enc<C> {
+    fn inner_iv_init(cipher: Self::Inner, iv: &cipher::Iv<Self>) -> Self {
+        Self {
+            cipher,
+            iv: iv.clone(),
+        }
+    }
+}
+
+impl<C: BlockEncrypt> Encrypt for CbcCs2Enc<C> {
+    fn encrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error> {
+        if buf.len() < C::BlockSize::USIZE {
+            return Err(Error);
+        }
+        let Self { cipher, iv } = self;
+        cipher.encrypt_with_backend(Closure { iv, buf });
+        Ok(())
+    }
+}
+
+struct Closure<'a, BS: ArrayLength<u8>> {
+    iv: GenericArray<u8, BS>,
+    buf: InOutBuf<'a, 'a, u8>,
+}
+
+impl<BS: ArrayLength<u8>> BlockSizeUser for Closure<'_, BS> {
+    type BlockSize = BS;
+}
+
+impl<BS: ArrayLength<u8>> BlockClosure for Closure<'_, BS> {
+    fn call<B: BlockBackend<BlockSize = BS>>(self, cipher: &mut B) {
+        let Self { mut iv, mut buf } = self;
+        let (mut blocks, mut tail) = buf.reborrow().into_chunks();
+
+        cbc_enc(cipher, &mut iv, blocks.reborrow());
+
+        if tail.is_empty() {
+            return;
+        }
+
+        let mut block = Block::<B>::default();
+        block[..tail.len()].copy_from_slice(tail.get_in());
+        xor(&mut block, &iv);
+        cipher.proc_block_inplace(&mut block);
+
+        let penult_block = core::mem::replace(blocks.get_out().last_mut().unwrap(), block);
+        let tail_val = &penult_block[..tail.len()];
+        tail.get_out().copy_from_slice(tail_val);
+    }
+}
diff --git a/cts/src/cbc_cs3_dec.rs b/cts/src/cbc_cs3_dec.rs
new file mode 100644
index 0000000..dafc509
--- /dev/null
+++ b/cts/src/cbc_cs3_dec.rs
@@ -0,0 +1,82 @@
+use crate::{cbc_dec, xor, Decrypt, Error};
+use cipher::{
+    crypto_common::InnerUser, generic_array::GenericArray, inout::InOutBuf, typenum::Unsigned,
+    ArrayLength, Block, BlockBackend, BlockClosure, BlockDecrypt, BlockSizeUser, InnerIvInit,
+    IvSizeUser,
+};
+
+/// The CBC-CS-3 ciphertext stealing mode decryptor.
+#[derive(Clone)]
+pub struct CbcCs3Dec<C: BlockDecrypt> {
+    cipher: C,
+    iv: Block<C>,
+}
+
+impl<C: BlockDecrypt> InnerUser for CbcCs3Dec<C> {
+    type Inner = C;
+}
+
+impl<C: BlockDecrypt> IvSizeUser for CbcCs3Dec<C> {
+    type IvSize = C::BlockSize;
+}
+
+impl<C: BlockDecrypt> InnerIvInit for CbcCs3Dec<C> {
+    fn inner_iv_init(cipher: Self::Inner, iv: &cipher::Iv<Self>) -> Self {
+        Self {
+            cipher,
+            iv: iv.clone(),
+        }
+    }
+}
+
+impl<C: BlockDecrypt> Decrypt for CbcCs3Dec<C> {
+    fn decrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error> {
+        if buf.len() < C::BlockSize::USIZE {
+            return Err(Error);
+        }
+        let Self { cipher, iv } = self;
+        cipher.decrypt_with_backend(Closure { iv, buf });
+        Ok(())
+    }
+}
+
+struct Closure<'a, BS: ArrayLength<u8>> {
+    iv: GenericArray<u8, BS>,
+    buf: InOutBuf<'a, 'a, u8>,
+}
+
+impl<BS: ArrayLength<u8>> BlockSizeUser for Closure<'_, BS> {
+    type BlockSize = BS;
+}
+
+impl<BS: ArrayLength<u8>> BlockClosure for Closure<'_, BS> {
+    fn call<B: BlockBackend<BlockSize = BS>>(self, cipher: &mut B) {
+        let Self { mut iv, buf } = self;
+
+        let bs = B::BlockSize::USIZE;
+        let blocks_len = buf.len().div_ceil(bs);
+        let main_blocks = blocks_len.saturating_sub(2);
+
+        let (blocks, mut tail) = buf.split_at(bs * main_blocks);
+        let (blocks, rem) = blocks.into_chunks();
+        debug_assert_eq!(rem.len(), 0);
+
+        cbc_dec(cipher, &mut iv, blocks);
+
+        let n = tail.len() - bs;
+        let mut block1 = GenericArray::clone_from_slice(&tail.get_in()[..bs]);
+        cipher.proc_block_inplace(&mut block1);
+
+        let mut block2 = GenericArray::<u8, BS>::default();
+        block2[..n].copy_from_slice(&tail.get_in()[bs..]);
+        block2[n..].copy_from_slice(&block1[n..]);
+        xor(&mut block1, &block2);
+
+        cipher.proc_block_inplace(&mut block2);
+        xor(&mut block2, &iv);
+
+        let (l, r) = tail.get_out().split_at_mut(bs);
+        l.copy_from_slice(&block2);
+        r.copy_from_slice(&block1[..n]);
+    }
+}
diff --git a/cts/src/cbc_cs3_enc.rs b/cts/src/cbc_cs3_enc.rs
new file mode 100644
index 0000000..e00bebc
--- /dev/null
+++ b/cts/src/cbc_cs3_enc.rs
@@ -0,0 +1,77 @@
+use crate::{cbc_enc, xor, Encrypt, Error};
+use cipher::{
+    crypto_common::InnerUser, generic_array::GenericArray, inout::InOutBuf, typenum::Unsigned,
+    ArrayLength, Block, BlockBackend, BlockClosure, BlockEncrypt, BlockSizeUser, InnerIvInit,
+    IvSizeUser,
+};
+
+/// The CBC-CS-3 ciphertext stealing mode encryptor.
+#[derive(Clone)]
+pub struct CbcCs3Enc<C: BlockEncrypt> {
+    cipher: C,
+    iv: Block<C>,
+}
+
+impl<C: BlockEncrypt> InnerUser for CbcCs3Enc<C> {
+    type Inner = C;
+}
+
+impl<C: BlockEncrypt> IvSizeUser for CbcCs3Enc<C> {
+    type IvSize = C::BlockSize;
+}
+
+impl<C: BlockEncrypt> InnerIvInit for CbcCs3Enc<C> {
+    fn inner_iv_init(cipher: Self::Inner, iv: &cipher::Iv<Self>) -> Self {
+        Self {
+            cipher,
+            iv: iv.clone(),
+        }
+    }
+}
+
+impl<C: BlockEncrypt> Encrypt for CbcCs3Enc<C> {
+    fn encrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error> {
+        if buf.len() < C::BlockSize::USIZE {
+            return Err(Error);
+        }
+        let Self { cipher, iv } = self;
+        cipher.encrypt_with_backend(Closure { iv, buf });
+        Ok(())
+    }
+}
+
+struct Closure<'a, BS: ArrayLength<u8>> {
+    iv: GenericArray<u8, BS>,
+    buf: InOutBuf<'a, 'a, u8>,
+}
+
+impl<BS: ArrayLength<u8>> BlockSizeUser for Closure<'_, BS> {
+    type BlockSize = BS;
+}
+
+impl<BS: ArrayLength<u8>> BlockClosure for Closure<'_, BS> {
+    fn call<B: BlockBackend<BlockSize = BS>>(self, cipher: &mut B) {
+        let Self { mut iv, mut buf } = self;
+        let (mut blocks, mut tail) = buf.reborrow().into_chunks();
+
+        cbc_enc(cipher, &mut iv, blocks.reborrow());
+
+        if tail.is_empty() && blocks.len() > 1 {
+            let blocks = blocks.get_out();
+            let (last, rest) = blocks.split_last_mut().unwrap();
+            let (penultimate, _) = rest.split_last_mut().unwrap();
+            core::mem::swap(penultimate, last);
+        } else {
+            let mut block = Block::<B>::default();
+            block[..tail.len()].copy_from_slice(tail.get_in());
+            xor(&mut block, &iv);
+            cipher.proc_block_inplace(&mut block);
+
+            let penult_block = blocks.get_out().last_mut().unwrap();
+            let val = core::mem::replace(penult_block, block);
+
+            let tail_val = &val[..tail.len()];
+            tail.get_out().copy_from_slice(tail_val);
+        }
+    }
+}
diff --git a/cts/src/ecb_cs1_dec.rs b/cts/src/ecb_cs1_dec.rs
new file mode 100644
index 0000000..5aeaf02
--- /dev/null
+++ b/cts/src/ecb_cs1_dec.rs
@@ -0,0 +1,86 @@
+use super::{ecb_dec, Decrypt, Error};
+use cipher::{
+    crypto_common::{InnerInit, InnerUser},
+    inout::InOutBuf,
+    typenum::Unsigned,
+    ArrayLength, Block, BlockBackend, BlockClosure, BlockDecrypt, BlockSizeUser, IvSizeUser,
+};
+use core::marker::PhantomData;
+
+/// The ECB-CS-1 ciphertext stealing mode decryptor.
+#[derive(Clone)]
+pub struct EcbCs1Dec<C: BlockDecrypt> {
+    cipher: C,
+}
+
+impl<C: BlockDecrypt> InnerUser for EcbCs1Dec<C> {
+    type Inner = C;
+}
+
+impl<C: BlockDecrypt> IvSizeUser for EcbCs1Dec<C> {
+    type IvSize = C::BlockSize;
+}
+
+impl<C: BlockDecrypt> InnerInit for EcbCs1Dec<C> {
+    fn inner_init(cipher: Self::Inner) -> Self {
+        Self { cipher }
+    }
+}
+
+impl<C: BlockDecrypt> Decrypt for EcbCs1Dec<C> {
+    fn decrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error> {
+        if buf.len() < C::BlockSize::USIZE {
+            return Err(Error);
+        }
+        self.cipher.decrypt_with_backend(Closure {
+            buf,
+            _pd: PhantomData,
+        });
+        Ok(())
+    }
+}
+
+struct Closure<'a, BS: ArrayLength<u8>> {
+    buf: InOutBuf<'a, 'a, u8>,
+    _pd: PhantomData<BS>,
+}
+
+impl<BS: ArrayLength<u8>> BlockSizeUser for Closure<'_, BS> {
+    type BlockSize = BS;
+}
+
+impl<BS: ArrayLength<u8>> BlockClosure for Closure<'_, BS> {
+    fn call<B: BlockBackend<BlockSize = BS>>(self, cipher: &mut B) {
+        let Self { mut buf, _pd } = self;
+
+        let (mut blocks, tail) = buf.reborrow().into_chunks();
+
+        if !tail.is_empty() {
+            let mid = blocks.len() - 1;
+            blocks = blocks.split_at(mid).0;
+        };
+
+        ecb_dec(cipher, blocks);
+
+        if tail.is_empty() {
+            return;
+        }
+
+        let tail_len = tail.len();
+        let bs = B::BlockSize::USIZE;
+        let mid = buf.len() - (bs + tail_len);
+        let mut rem = buf.split_at(mid).1;
+
+        let n = rem.len() - bs;
+        let mut block1 = Block::<B>::clone_from_slice(&rem.get_in()[..bs]);
+        let mut block2 = Block::<B>::clone_from_slice(&rem.get_in()[n..]);
+
+        cipher.proc_block_inplace(&mut block2);
+        block1[n..].copy_from_slice(&block2[n..]);
+
+        cipher.proc_block_inplace(&mut block1);
+
+        rem.get_out()[..bs].copy_from_slice(&block1);
+        rem.get_out()[bs..].copy_from_slice(&block2[..n]);
+    }
+}
diff --git a/cts/src/ecb_cs1_enc.rs b/cts/src/ecb_cs1_enc.rs
new file mode 100644
index 0000000..ddc243d
--- /dev/null
+++ b/cts/src/ecb_cs1_enc.rs
@@ -0,0 +1,75 @@
+use crate::{ecb_enc, Encrypt, Error};
+use cipher::{
+    crypto_common::{InnerInit, InnerUser},
+    inout::InOutBuf,
+    typenum::Unsigned,
+    ArrayLength, Block, BlockBackend, BlockClosure, BlockEncrypt, BlockSizeUser, IvSizeUser,
+};
+use core::marker::PhantomData;
+
+/// The ECB-CS-1 ciphertext stealing mode encryptor.
+#[derive(Clone)]
+pub struct EcbCs1Enc<C: BlockEncrypt> {
+    cipher: C,
+}
+
+impl<C: BlockEncrypt> InnerUser for EcbCs1Enc<C> {
+    type Inner = C;
+}
+
+impl<C: BlockEncrypt> IvSizeUser for EcbCs1Enc<C> {
+    type IvSize = C::BlockSize;
+}
+
+impl<C: BlockEncrypt> InnerInit for EcbCs1Enc<C> {
+    fn inner_init(cipher: Self::Inner) -> Self {
+        Self { cipher }
+    }
+}
+
+impl<C: BlockEncrypt> Encrypt for EcbCs1Enc<C> {
+    fn encrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error> {
+        if buf.len() < C::BlockSize::USIZE {
+            return Err(Error);
+        }
+        self.cipher.encrypt_with_backend(Closure {
+            buf,
+            _pd: PhantomData,
+        });
+        Ok(())
+    }
+}
+
+struct Closure<'a, BS: ArrayLength<u8>> {
+    buf: InOutBuf<'a, 'a, u8>,
+    _pd: PhantomData<BS>,
+}
+
+impl<BS: ArrayLength<u8>> BlockSizeUser for Closure<'_, BS> {
+    type BlockSize = BS;
+}
+
+impl<BS: ArrayLength<u8>> BlockClosure for Closure<'_, BS> {
+    fn call<B: BlockBackend<BlockSize = BS>>(self, cipher: &mut B) {
+        let Self { mut buf, _pd } = self;
+        let (mut blocks, tail) = buf.reborrow().into_chunks();
+
+        ecb_enc(cipher, blocks.reborrow());
+
+        if tail.is_empty() {
+            return;
+        }
+
+        let last_block = blocks.get_out().last_mut().unwrap();
+        let mut block = Block::<B>::default();
+
+        let n = tail.len();
+
+        block[..n].copy_from_slice(tail.get_in());
+        block[n..].copy_from_slice(&last_block[n..]);
+        cipher.proc_block_inplace(&mut block);
+
+        let pos = buf.len() - block.len();
+        buf.get_out()[pos..].copy_from_slice(&block);
+    }
+}
diff --git a/cts/src/ecb_cs2_dec.rs b/cts/src/ecb_cs2_dec.rs
new file mode 100644
index 0000000..0bb2010
--- /dev/null
+++ b/cts/src/ecb_cs2_dec.rs
@@ -0,0 +1,76 @@
+use crate::{ecb_dec, Decrypt, Error};
+use cipher::{
+    crypto_common::{InnerInit, InnerUser},
+    inout::InOutBuf,
+    typenum::Unsigned,
+    ArrayLength, Block, BlockBackend, BlockClosure, BlockDecrypt, BlockSizeUser, IvSizeUser,
+};
+use core::marker::PhantomData;
+
+/// The ECB-CS-2 ciphertext stealing mode decryptor.
+#[derive(Clone)]
+pub struct EcbCs2Dec<C: BlockDecrypt> {
+    cipher: C,
+}
+
+impl<C: BlockDecrypt> InnerUser for EcbCs2Dec<C> {
+    type Inner = C;
+}
+
+impl<C: BlockDecrypt> IvSizeUser for EcbCs2Dec<C> {
+    type IvSize = C::BlockSize;
+}
+
+impl<C: BlockDecrypt> InnerInit for EcbCs2Dec<C> {
+    fn inner_init(cipher: Self::Inner) -> Self {
+        Self { cipher }
+    }
+}
+
+impl<C: BlockDecrypt> Decrypt for EcbCs2Dec<C> {
+    fn decrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error> {
+        if buf.len() < C::BlockSize::USIZE {
+            return Err(Error);
+        }
+        self.cipher.decrypt_with_backend(Closure {
+            buf,
+            _pd: PhantomData,
+        });
+        Ok(())
+    }
+}
+
+struct Closure<'a, BS: ArrayLength<u8>> {
+    buf: InOutBuf<'a, 'a, u8>,
+    _pd: PhantomData<BS>,
+}
+
+impl<BS: ArrayLength<u8>> BlockSizeUser for Closure<'_, BS> {
+    type BlockSize = BS;
+}
+
+impl<BS: ArrayLength<u8>> BlockClosure for Closure<'_, BS> {
+    fn call<B: BlockBackend<BlockSize = BS>>(self, cipher: &mut B) {
+        let Self { mut buf, _pd } = self;
+
+        let (mut blocks, mut tail) = buf.reborrow().into_chunks();
+
+        ecb_dec(cipher, blocks.reborrow());
+
+        if tail.is_empty() {
+            return;
+        }
+
+        let last_block = blocks.get_out().last_mut().unwrap();
+
+        let tail_len = tail.len();
+        let mut block = Block::<B>::default();
+        block[..tail_len].copy_from_slice(tail.get_in());
+        block[tail_len..].copy_from_slice(&last_block[tail_len..]);
+        tail.get_out().copy_from_slice(&last_block[..tail_len]);
+
+        cipher.proc_block_inplace(&mut block);
+
+        *last_block = block;
+    }
+}
diff --git a/cts/src/ecb_cs2_enc.rs b/cts/src/ecb_cs2_enc.rs
new file mode 100644
index 0000000..b910789
--- /dev/null
+++ b/cts/src/ecb_cs2_enc.rs
@@ -0,0 +1,75 @@
+use crate::{ecb_enc, Encrypt, Error};
+use cipher::{
+    crypto_common::{InnerInit, InnerUser},
+    inout::InOutBuf,
+    typenum::Unsigned,
+    ArrayLength, Block, BlockBackend, BlockClosure, BlockEncrypt, BlockSizeUser, IvSizeUser,
+};
+use core::marker::PhantomData;
+
+/// The ECB-CS-2 ciphertext stealing mode encryptor.
+#[derive(Clone)]
+pub struct EcbCs2Enc<C: BlockEncrypt> {
+    cipher: C,
+}
+
+impl<C: BlockEncrypt> InnerUser for EcbCs2Enc<C> {
+    type Inner = C;
+}
+
+impl<C: BlockEncrypt> IvSizeUser for EcbCs2Enc<C> {
+    type IvSize = C::BlockSize;
+}
+
+impl<C: BlockEncrypt> InnerInit for EcbCs2Enc<C> {
+    fn inner_init(cipher: Self::Inner) -> Self {
+        Self { cipher }
+    }
+}
+
+impl<C: BlockEncrypt> Encrypt for EcbCs2Enc<C> {
+    fn encrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error> {
+        if buf.len() < C::BlockSize::USIZE {
+            return Err(Error);
+        }
+        self.cipher.encrypt_with_backend(Closure {
+            buf,
+            _pd: PhantomData,
+        });
+        Ok(())
+    }
+}
+
+struct Closure<'a, BS: ArrayLength<u8>> {
+    buf: InOutBuf<'a, 'a, u8>,
+    _pd: PhantomData<BS>,
+}
+
+impl<BS: ArrayLength<u8>> BlockSizeUser for Closure<'_, BS> {
+    type BlockSize = BS;
+}
+
+impl<BS: ArrayLength<u8>> BlockClosure for Closure<'_, BS> {
+    fn call<B: BlockBackend<BlockSize = BS>>(self, cipher: &mut B) {
+        let Self { mut buf, _pd } = self;
+        let (mut blocks, mut tail) = buf.reborrow().into_chunks();
+
+        ecb_enc(cipher, blocks.reborrow());
+
+        if tail.is_empty() {
+            return;
+        }
+
+        let last_block = blocks.get_out().last_mut().unwrap();
+
+        let n = tail.len();
+
+        let mut block = Block::<B>::default();
+        block[..n].copy_from_slice(tail.get_in());
+        block[n..].copy_from_slice(&last_block[n..]);
+        cipher.proc_block_inplace(&mut block);
+
+        tail.get_out().copy_from_slice(&last_block[..n]);
+        *last_block = block;
+    }
+}
diff --git a/cts/src/ecb_cs3_dec.rs b/cts/src/ecb_cs3_dec.rs
new file mode 100644
index 0000000..124883d
--- /dev/null
+++ b/cts/src/ecb_cs3_dec.rs
@@ -0,0 +1,78 @@
+use crate::{ecb_dec, Decrypt, Error};
+use cipher::{
+    crypto_common::{InnerInit, InnerUser},
+    inout::InOutBuf,
+    typenum::Unsigned,
+    ArrayLength, Block, BlockBackend, BlockClosure, BlockDecrypt, BlockSizeUser, IvSizeUser,
+};
+use core::marker::PhantomData;
+
+/// The ECB-CS-3 ciphertext stealing mode decryptor.
+#[derive(Clone)]
+pub struct EcbCs3Dec<C: BlockDecrypt> {
+    cipher: C,
+}
+
+impl<C: BlockDecrypt> InnerUser for EcbCs3Dec<C> {
+    type Inner = C;
+}
+
+impl<C: BlockDecrypt> IvSizeUser for EcbCs3Dec<C> {
+    type IvSize = C::BlockSize;
+}
+
+impl<C: BlockDecrypt> InnerInit for EcbCs3Dec<C> {
+    fn inner_init(cipher: Self::Inner) -> Self {
+        Self { cipher }
+    }
+}
+
+impl<C: BlockDecrypt> Decrypt for EcbCs3Dec<C> {
+    fn decrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error> {
+        if buf.len() < C::BlockSize::USIZE {
+            return Err(Error);
+        }
+        self.cipher.decrypt_with_backend(Closure {
+            buf,
+            _pd: PhantomData,
+        });
+        Ok(())
+    }
+}
+
+struct Closure<'a, BS: ArrayLength<u8>> {
+    buf: InOutBuf<'a, 'a, u8>,
+    _pd: PhantomData<BS>,
+}
+
+impl<BS: ArrayLength<u8>> BlockSizeUser for Closure<'_, BS> {
+    type BlockSize = BS;
+}
+
+impl<BS: ArrayLength<u8>> BlockClosure for Closure<'_, BS> {
+    fn call<B: BlockBackend<BlockSize = BS>>(self, cipher: &mut B) {
+        let Self { mut buf, _pd } = self;
+
+        let (mut blocks, mut tail) = buf.reborrow().into_chunks();
+
+        ecb_dec(cipher, blocks.reborrow());
+
+        if tail.is_empty() && blocks.len() > 1 {
+            let blocks = blocks.get_out();
+            let (last, rest) = blocks.split_last_mut().unwrap();
+            let (penultimate, _) = rest.split_last_mut().unwrap();
+            core::mem::swap(penultimate, last);
+        } else {
+            let last_block = blocks.get_out().last_mut().unwrap();
+
+            let n = tail.len();
+            let mut block = Block::<B>::default();
+            block[..n].copy_from_slice(tail.get_in());
+            block[n..].copy_from_slice(&last_block[n..]);
+            tail.get_out().copy_from_slice(&last_block[..n]);
+
+            cipher.proc_block_inplace(&mut block);
+            *last_block = block;
+        }
+    }
+}
diff --git a/cts/src/ecb_cs3_enc.rs b/cts/src/ecb_cs3_enc.rs
new file mode 100644
index 0000000..4b1a230
--- /dev/null
+++ b/cts/src/ecb_cs3_enc.rs
@@ -0,0 +1,78 @@
+use crate::{ecb_enc, Encrypt, Error};
+use cipher::{
+    crypto_common::{InnerInit, InnerUser},
+    inout::InOutBuf,
+    typenum::Unsigned,
+    ArrayLength, Block, BlockBackend, BlockClosure, BlockEncrypt, BlockSizeUser, IvSizeUser,
+};
+use core::marker::PhantomData;
+
+/// The ECB-CS-3 ciphertext stealing mode encryptor.
+#[derive(Clone)]
+pub struct EcbCs3Enc<C: BlockEncrypt> {
+    cipher: C,
+}
+
+impl<C: BlockEncrypt> InnerUser for EcbCs3Enc<C> {
+    type Inner = C;
+}
+
+impl<C: BlockEncrypt> IvSizeUser for EcbCs3Enc<C> {
+    type IvSize = C::BlockSize;
+}
+
+impl<C: BlockEncrypt> InnerInit for EcbCs3Enc<C> {
+    fn inner_init(cipher: Self::Inner) -> Self {
+        Self { cipher }
+    }
+}
+
+impl<C: BlockEncrypt> Encrypt for EcbCs3Enc<C> {
+    fn encrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error> {
+        if buf.len() < C::BlockSize::USIZE {
+            return Err(Error);
+        }
+        self.cipher.encrypt_with_backend(Closure {
+            buf,
+            _pd: PhantomData,
+        });
+        Ok(())
+    }
+}
+
+struct Closure<'a, BS: ArrayLength<u8>> {
+    buf: InOutBuf<'a, 'a, u8>,
+    _pd: PhantomData<BS>,
+}
+
+impl<BS: ArrayLength<u8>> BlockSizeUser for Closure<'_, BS> {
+    type BlockSize = BS;
+}
+
+impl<BS: ArrayLength<u8>> BlockClosure for Closure<'_, BS> {
+    fn call<B: BlockBackend<BlockSize = BS>>(self, cipher: &mut B) {
+        let Self { mut buf, _pd } = self;
+        let (mut blocks, mut tail) = buf.reborrow().into_chunks();
+
+        ecb_enc(cipher, blocks.reborrow());
+
+        if tail.is_empty() && blocks.len() > 1 {
+            let blocks = blocks.get_out();
+            let (last, rest) = blocks.split_last_mut().unwrap();
+            let (penultimate, _) = rest.split_last_mut().unwrap();
+            core::mem::swap(penultimate, last);
+        } else {
+            let last_block = blocks.get_out().last_mut().unwrap();
+
+            let n = tail.len();
+
+            let mut block = Block::<B>::default();
+            block[..n].copy_from_slice(tail.get_in());
+            block[n..].copy_from_slice(&last_block[n..]);
+            cipher.proc_block_inplace(&mut block);
+
+            tail.get_out().copy_from_slice(&last_block[..n]);
+            *last_block = block;
+        }
+    }
+}
diff --git a/cts/src/lib.rs b/cts/src/lib.rs
new file mode 100644
index 0000000..a201ac5
--- /dev/null
+++ b/cts/src/lib.rs
@@ -0,0 +1,176 @@
+#![no_std]
+#![doc = include_str!("../README.md")]
+#![doc(
+    html_logo_url = "https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg",
+    html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg"
+)]
+#![deny(unsafe_code)]
+#![cfg_attr(docsrs, feature(doc_cfg))]
+#![warn(missing_docs, rust_2018_idioms)]
+
+pub use cipher;
+
+pub use cipher::{KeyInit, KeyIvInit};
+
+mod cbc_cs1_enc;
+pub use cbc_cs1_enc::CbcCs1Enc;
+
+mod cbc_cs1_dec;
+pub use cbc_cs1_dec::CbcCs1Dec;
+
+mod cbc_cs2_enc;
+pub use cbc_cs2_enc::CbcCs2Enc;
+
+mod cbc_cs2_dec;
+pub use cbc_cs2_dec::CbcCs2Dec;
+
+mod cbc_cs3_enc;
+pub use cbc_cs3_enc::CbcCs3Enc;
+
+mod cbc_cs3_dec;
+pub use cbc_cs3_dec::CbcCs3Dec;
+
+mod ecb_cs1_enc;
+pub use ecb_cs1_enc::EcbCs1Enc;
+
+mod ecb_cs1_dec;
+pub use ecb_cs1_dec::EcbCs1Dec;
+
+mod ecb_cs2_enc;
+pub use ecb_cs2_enc::EcbCs2Enc;
+
+mod ecb_cs2_dec;
+pub use ecb_cs2_dec::EcbCs2Dec;
+
+mod ecb_cs3_enc;
+pub use ecb_cs3_enc::EcbCs3Enc;
+
+mod ecb_cs3_dec;
+pub use ecb_cs3_dec::EcbCs3Dec;
+
+use cipher::{
+    generic_array::{typenum::Unsigned, GenericArray},
+    inout::{InOutBuf, NotEqualError},
+    ArrayLength, Block, BlockBackend,
+};
+
+/// Error which indicates that message is smaller than cipher's block size.
+#[derive(Copy, Clone, Debug)]
+pub struct Error;
+
+/// Encryption functionality of CTS modes.
+pub trait Encrypt: Sized {
+    /// Encrypt `inout` buffer.
+    fn encrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error>;
+
+    /// Encrypt data in-place.
+    fn encrypt(self, buf: &mut [u8]) -> Result<(), Error> {
+        self.encrypt_inout(buf.into())
+    }
+
+    /// Encrypt data buffer-to-buffer.
+    fn encrypt_b2b(self, in_buf: &[u8], out_buf: &mut [u8]) -> Result<(), Error> {
+        InOutBuf::new(in_buf, out_buf)
+            .map_err(|NotEqualError| Error)
+            .and_then(|buf| self.encrypt_inout(buf))
+    }
+}
+
+/// Decryption functionality of CTS modes.
+pub trait Decrypt: Sized {
+    /// Decrypt `inout` buffer.
+    fn decrypt_inout(self, buf: InOutBuf<'_, '_, u8>) -> Result<(), Error>;
+
+    /// Decrypt data in-place.
+    fn decrypt(self, buf: &mut [u8]) -> Result<(), Error> {
+        self.decrypt_inout(buf.into())
+    }
+
+    /// Decrypt data buffer-to-buffer.
+    fn decrypt_b2b(self, in_buf: &[u8], out_buf: &mut [u8]) -> Result<(), Error> {
+        InOutBuf::new(in_buf, out_buf)
+            .map_err(|NotEqualError| Error)
+            .and_then(|buf| self.decrypt_inout(buf))
+    }
+}
+
+fn ecb_enc<B: BlockBackend>(cipher: &mut B, mut blocks: InOutBuf<'_, '_, Block<B>>) {
+    if B::ParBlocksSize::USIZE > 1 {
+        let (par_blocks, rem_blocks) = blocks.into_chunks();
+        blocks = rem_blocks;
+        for blocks in par_blocks {
+            cipher.proc_par_blocks(blocks);
+        }
+    }
+    for block in blocks {
+        cipher.proc_block(block);
+    }
+}
+
+fn ecb_dec<B: BlockBackend>(cipher: &mut B, mut blocks: InOutBuf<'_, '_, Block<B>>) {
+    if B::ParBlocksSize::USIZE > 1 {
+        let (par_blocks, rem_blocks) = blocks.into_chunks();
+        blocks = rem_blocks;
+        for blocks in par_blocks {
+            cipher.proc_par_blocks(blocks);
+        }
+    }
+    for block in blocks {
+        cipher.proc_block(block);
+    }
+}
+
+fn cbc_enc<B: BlockBackend>(
+    cipher: &mut B,
+    iv: &mut Block<B>,
+    mut blocks: InOutBuf<'_, '_, Block<B>>,
+) {
+    for mut block in blocks.reborrow() {
+        let mut t = block.clone_in();
+        xor(&mut t, iv);
+        cipher.proc_block_inplace(&mut t);
+        *iv = t.clone();
+        *block.get_out() = t;
+    }
+}
+
+fn cbc_dec<B: BlockBackend>(
+    cipher: &mut B,
+    iv: &mut Block<B>,
+    mut blocks: InOutBuf<'_, '_, Block<B>>,
+) {
+    if B::ParBlocksSize::USIZE > 1 {
+        let (par_blocks, rem_blocks) = blocks.into_chunks();
+        blocks = rem_blocks;
+
+        for mut blocks in par_blocks {
+            let in_blocks = blocks.clone_in();
+            let mut t = blocks.clone_in();
+
+            cipher.proc_par_blocks_inplace(&mut t);
+            let n = t.len();
+            xor(&mut t[0], iv);
+            for i in 1..n {
+                xor(&mut t[i], &in_blocks[i - 1])
+            }
+            *blocks.get_out() = t;
+            *iv = in_blocks[n - 1].clone();
+        }
+    }
+
+    for mut block in blocks {
+        let in_block = block.clone_in();
+        let mut t = block.clone_in();
+        cipher.proc_block_inplace(&mut t);
+        xor(&mut t, iv);
+        *block.get_out() = t;
+        *iv = in_block;
+    }
+}
+
+#[inline(always)]
+fn xor<N: ArrayLength<u8>>(out: &mut GenericArray<u8, N>, buf: &GenericArray<u8, N>) {
+    for (a, b) in out.iter_mut().zip(buf) {
+        *a ^= *b;
+    }
+}


Test patch:
diff --git a/cts/tests/aes128_roundtrip.rs b/cts/tests/aes128_roundtrip.rs
new file mode 100644
index 0000000..26b0810
--- /dev/null
+++ b/cts/tests/aes128_roundtrip.rs
@@ -0,0 +1,87 @@
+use aes::Aes128;
+use cts::{
+    cipher::{crypto_common::InnerInit, InnerIvInit, KeyInit},
+    Decrypt, Encrypt,
+};
+
+const KEY: [u8; 16] = [0x42; 16];
+const IV: [u8; 16] = [0x24; 16];
+
+const N: usize = 256;
+const MSG: [u8; N] = {
+    let mut res = [0u8; N];
+    let mut i = 0;
+    while i < N {
+        res[i] = i as u8;
+        i += 1;
+    }
+    res
+};
+
+macro_rules! impl_cbc_roundtrip {
+    ($name:ident, $enc:ident, $dec:ident) => {
+        #[test]
+        fn $name() {
+            let mut buf1 = [0u8; N];
+            let mut buf2 = [0u8; N];
+
+            let cipher = Aes128::new(&KEY.into());
+            for i in 16..MSG.len() {
+                let enc_mode = cts::$enc::inner_iv_init(&cipher, &IV.into());
+                let ct = &mut buf1[..i];
+                enc_mode.encrypt_b2b(&MSG[..i], ct).unwrap();
+
+                let dec_mode = cts::$dec::inner_iv_init(&cipher, &IV.into());
+                let pt = &mut buf2[..i];
+                dec_mode.decrypt_b2b(ct, pt).unwrap();
+                assert_eq!(pt, &MSG[..i]);
+
+                let enc_mode = cts::$enc::inner_iv_init(&cipher, &IV.into());
+                enc_mode.encrypt(pt).unwrap();
+                assert_eq!(pt, ct);
+
+                let dec_mode = cts::$dec::inner_iv_init(&cipher, &IV.into());
+                dec_mode.decrypt(pt).unwrap();
+                assert_eq!(pt, &MSG[..i]);
+            }
+        }
+    };
+}
+
+impl_cbc_roundtrip!(aes128_cbc_cs1_roundtrip, CbcCs1Enc, CbcCs1Dec);
+impl_cbc_roundtrip!(aes128_cbc_cs2_roundtrip, CbcCs2Enc, CbcCs2Dec);
+impl_cbc_roundtrip!(aes128_cbc_cs3_roundtrip, CbcCs3Enc, CbcCs3Dec);
+
+macro_rules! impl_ecb_roundtrip {
+    ($name:ident, $enc:ident, $dec:ident) => {
+        #[test]
+        fn $name() {
+            let mut buf1 = [0u8; N];
+            let mut buf2 = [0u8; N];
+
+            let cipher = Aes128::new(&KEY.into());
+            for i in 16..MSG.len() {
+                let enc_mode = cts::$enc::inner_init(&cipher);
+                let ct = &mut buf1[..i];
+                enc_mode.encrypt_b2b(&MSG[..i], ct).unwrap();
+
+                let dec_mode = cts::$dec::inner_init(&cipher);
+                let pt = &mut buf2[..i];
+                dec_mode.decrypt_b2b(ct, pt).unwrap();
+                assert_eq!(pt, &MSG[..i]);
+
+                let enc_mode = cts::$enc::inner_init(&cipher);
+                enc_mode.encrypt(pt).unwrap();
+                assert_eq!(pt, ct);
+
+                let dec_mode = cts::$dec::inner_init(&cipher);
+                dec_mode.decrypt(pt).unwrap();
+                assert_eq!(pt, &MSG[..i]);
+            }
+        }
+    };
+}
+
+impl_ecb_roundtrip!(aes128_ecb_cs1_roundtrip, EcbCs1Enc, EcbCs1Dec);
+impl_ecb_roundtrip!(aes128_ecb_cs2_roundtrip, EcbCs2Enc, EcbCs2Dec);
+impl_ecb_roundtrip!(aes128_ecb_cs3_roundtrip, EcbCs3Enc, EcbCs3Dec);
diff --git a/cts/tests/belt_ecb.rs b/cts/tests/belt_ecb.rs
new file mode 100644
index 0000000..dbed70f
--- /dev/null
+++ b/cts/tests/belt_ecb.rs
@@ -0,0 +1,93 @@
+//! Test vectors from STB 34.101.31-2020 (section А.4, tables A.9-10):
+//! https://apmi.bsu.by/assets/files/std/belt-spec371.pdf
+use belt_block::BeltBlock;
+use cts::{Decrypt, Encrypt, KeyInit};
+use hex_literal::hex;
+
+struct TestVector {
+    key: &'static [u8; 32],
+    pt: &'static [u8],
+    ct: &'static [u8],
+}
+
+static TEST_VECTORS: &[TestVector] = &[
+    TestVector {
+        key: &hex!(
+            "E9DEE72C 8F0C0FA6 2DDB49F4 6F739647"
+            "06075316 ED247A37 39CBA383 03A98BF6"
+        ),
+        pt: &hex!(
+            "B194BAC8 0A08F53B 366D008E 584A5DE4"
+            "8504FA9D 1BB6C7AC 252E72C2 02FDCE0D"
+            "5BE3D612 17B96181 FE6786AD 716B890B"
+        ),
+        ct: &hex!(
+            "69CCA1C9 3557C9E3 D66BC3E0 FA88FA6E"
+            "5F23102E F1097107 75017F73 806DA9DC"
+            "46FB2ED2 CE771F26 DCB5E5D1 569F9AB0"
+        ),
+    },
+    TestVector {
+        key: &hex!(
+            "E9DEE72C 8F0C0FA6 2DDB49F4 6F739647"
+            "06075316 ED247A37 39CBA383 03A98BF6"
+        ),
+        pt: &hex!(
+            "B194BAC8 0A08F53B 366D008E 584A5DE4"
+            "8504FA9D 1BB6C7AC 252E72C2 02FDCE0D"
+            "5BE3D612 17B96181 FE6786AD 716B89"
+        ),
+        ct: &hex!(
+            "69CCA1C9 3557C9E3 D66BC3E0 FA88FA6E"
+            "36F00CFE D6D1CA14 98C12798 F4BEB207"
+            "5F23102E F1097107 75017F73 806DA9"
+        ),
+    },
+    TestVector {
+        key: &hex!(
+            "92BD9B1C E5D14101 5445FBC9 5E4D0EF2"
+            "682080AA 227D642F 2687F934 90405511"
+        ),
+        pt: &hex!(
+            "0DC53006 00CAB840 B38448E5 E993F421"
+            "E55A239F 2AB5C5D5 FDB6E81B 40938E2A"
+            "54120CA3 E6E19C7A D750FC35 31DAEAB7"
+        ),
+        ct: &hex!(
+            "E12BDC1A E28257EC 703FCCF0 95EE8DF1"
+            "C1AB7638 9FE678CA F7C6F860 D5BB9C4F"
+            "F33C657B 637C306A DD4EA779 9EB23D31"
+        ),
+    },
+    TestVector {
+        key: &hex!(
+            "92BD9B1C E5D14101 5445FBC9 5E4D0EF2"
+            "682080AA 227D642F 2687F934 90405511"
+        ),
+        pt: &hex!(
+            "0DC53006 00CAB840 B38448E5 E993F421"
+            "5780A6E2 B69EAFBB 258726D7 B6718523"
+            "E55A239F"
+        ),
+        ct: &hex!(
+            "E12BDC1A E28257EC 703FCCF0 95EE8DF1"
+            "C1AB7638 9FE678CA F7C6F860 D5BB9C4F"
+            "F33C657B"
+        ),
+    },
+];
+
+#[test]
+fn belt_ecb() {
+    let mut buf = [0u8; 48];
+    for &TestVector { key, pt, ct } in TEST_VECTORS {
+        let buf = &mut buf[..pt.len()];
+        let enc_mode = cts::EcbCs2Enc::<BeltBlock>::new(key.into());
+        enc_mode.encrypt_b2b(pt, buf).unwrap();
+        assert_eq!(buf, ct);
+
+        let dec_mode = cts::EcbCs2Dec::<BeltBlock>::new(key.into());
+        dec_mode.decrypt(buf).unwrap();
+        assert_eq!(buf, pt);
+    }
+}
diff --git a/cts/tests/rfc3962.rs b/cts/tests/rfc3962.rs
new file mode 100644
index 0000000..84a3bee
--- /dev/null
+++ b/cts/tests/rfc3962.rs
@@ -0,0 +1,98 @@
+//! Test vectors from RFC 3962: https://www.rfc-editor.org/rfc/rfc3962
+use aes::Aes128;
+use cipher::{InnerIvInit, KeyInit};
+use cts::{Decrypt, Encrypt};
+use hex_literal::hex;
+
+const KEY: [u8; 16] = hex!("636869636b656e207465726979616b69");
+const IV: [u8; 16] = [0u8; 16];
+
+static TEST_VECTORS: &[(&[u8], &[u8])] = &[
+    (
+        &hex!(
+            "4920776f756c64206c696b6520746865"
+            "20"
+        ),
+        &hex!(
+            "c6353568f2bf8cb4d8a580362da7ff7f"
+            "97"
+        ),
+    ),
+    (
+        &hex!(
+            "4920776f756c64206c696b6520746865"
+            "2047656e6572616c20476175277320"
+        ),
+        &hex!(
+            "fc00783e0efdb2c1d445d4c8eff7ed22"
+            "97687268d6ecccc0c07b25e25ecfe5"
+        ),
+    ),
+    (
+        &hex!(
+            "4920776f756c64206c696b6520746865"
+            "2047656e6572616c2047617527732043"
+        ),
+        &hex!(
+            "39312523a78662d5be7fcbcc98ebf5a8"
+            "97687268d6ecccc0c07b25e25ecfe584"
+        ),
+    ),
+    (
+        &hex!(
+            "4920776f756c64206c696b6520746865"
+            "2047656e6572616c2047617527732043"
+            "6869636b656e2c20706c656173652c"
+        ),
+        &hex!(
+            "97687268d6ecccc0c07b25e25ecfe584"
+            "b3fffd940c16a18c1b5549d2f838029e"
+            "39312523a78662d5be7fcbcc98ebf5"
+        ),
+    ),
+    (
+        &hex!(
+            "4920776f756c64206c696b6520746865"
+            "2047656e6572616c2047617527732043"
+            "6869636b656e2c20706c656173652c20"
+        ),
+        &hex!(
+            "97687268d6ecccc0c07b25e25ecfe584"
+            "9dad8bbb96c4cdc03bc103e1a194bbd8"
+            "39312523a78662d5be7fcbcc98ebf5a8"
+        ),
+    ),
+    (
+        &hex!(
+            "4920776f756c64206c696b6520746865"
+            "2047656e6572616c2047617527732043"
+            "6869636b656e2c20706c656173652c20"
+            "616e6420776f6e746f6e20736f75702e"
+        ),
+        &hex!(
+            "97687268d6ecccc0c07b25e25ecfe584"
+            "39312523a78662d5be7fcbcc98ebf5a8"
+            "4807efe836ee89a526730dbc2f7bc840"
+            "9dad8bbb96c4cdc03bc103e1a194bbd8"
+        ),
+    ),
+];
+
+#[test]
+fn rfc3962() {
+    let cipher = Aes128::new(&KEY.into());
+    let iv = IV.into();
+
+    let mut buf = [0u8; 64];
+    for &(input, output) in TEST_VECTORS {
+        let buf = &mut buf[..input.len()];
+
+        let enc_mode = cts::CbcCs3Enc::inner_iv_init(&cipher, &iv);
+        enc_mode.encrypt_b2b(input, buf).unwrap();
+        assert_eq!(buf, output);
+
+        let dec_mode = cts::CbcCs3Dec::inner_iv_init(&cipher, &iv);
+        dec_mode.decrypt_b2b(output, buf).unwrap();
+        assert_eq!(buf, input);
+    }
+}