# PKCS

Public Key Cryptography Standards (PKCS) are a group of public-key cryptography standards devised and published by RSA Security LLC, starting in the early 1990s. The company published the standards to promote the use of the cryptography techniques for which they had patents, such as the RSA algorithm, the Schnorr signature algorithm and several others. Though not industry standards (because the company retained control over them), some of the standards have begun to move into the "standards track" processes of relevant standards organizations in recent years, such as the IETF and the PKIX working group.
Key Updates (2023–2024):
* Integration of PKCS #7 and PKCS #12 into broader standards like S/MIME and TLS.
* Evolution of PKCS #11 to support newer hardware and cloud services.
* Involvement of PKCS standards in post-quantum cryptography efforts, with NIST's ongoing standardization.
* Growing adoption of PKCS standards in the context of blockchain and digital assets.
PKCS Standards Summary :
| | Version | Name | Comments |
| PKCS #1 | 2.2 | RSA Cryptography Standard | See RFC 8017. Defines the mathematical properties and format of RSA public and private keys (ASN.1-encoded in clear-text), and the basic algorithms and encoding/padding schemes for performing RSA encryption, decryption, and producing and verifying signatures. |
| PKCS #2 | - | Withdrawn | No longer active as of 2010. Covered RSA encryption of message digests; subsequently merged into PKCS #1. |
| PKCS #3 | 1.4 | Diffie–Hellman Key Agreement Standard | A cryptographic protocol that allows two parties that have no prior knowledge of each other to jointly establish a shared secret key over an insecure communications channel. |
| PKCS #4 | - | Withdrawn | No longer active as of 2010. Covered RSA key syntax; subsequently merged into PKCS #1. |
| PKCS #5 | 2.1 | Password-based Encryption Standard | See RFC 8018 and PBKDF2. |
| PKCS #6 | 1.5 | Extended-Certificate Syntax Standard | Defines extensions to the old v1 X.509 certificate specification. Obsoleted by v3 of the same. |
| PKCS #7 | 1.5 | Cryptographic Message Syntax Standard | See RFC 2315. Used to sign and/or encrypt messages under a PKI. Used also for certificate dissemination (for instance as a response to a PKCS #10 message). Formed the basis for S/MIME, which is as of 2010 based on RFC 5652, an updated Cryptographic Message Syntax Standard (CMS). Often used for single sign-on. |
| PKCS #8 | 1.2 | Private-Key Information Syntax Standard | See RFC 5958. Used to carry private certificate keypairs (encrypted or unencrypted). |
| PKCS #9 | 2.0 | Selected Attribute Types | See RFC 2985. Defines selected attribute types for use in PKCS #6 extended certificates, PKCS #7 digitally signed messages, PKCS #8 private-key information, and PKCS #10 certificate-signing requests. |
| PKCS #10 | 1.7 | Certification Request Standard | See RFC 2986. Format of messages sent to a certification authority to request certification of a public key. See certificate signing request. |
| PKCS #11 | 3.0 | Cryptographic Token Interface | Also known as "Cryptoki". An API defining a generic interface to cryptographic tokens (see also hardware security module). Often used in single sign-on, public-key cryptography and disk encryption systems. RSA Security has turned over further development of the PKCS #11 standard to the OASIS PKCS 11 Technical Committee. |
| PKCS #12 | 1.1 | Personal Information Exchange Syntax Standard | See RFC 7292. Defines a file format commonly used to store private keys with accompanying public key certificates, protected with a password-based symmetric key. PFX is a predecessor to PKCS #12. This container format can contain multiple embedded objects, such as multiple certificates. Usually protected/encrypted with a password. Usable as a format for the Java KeyStore and to establish client authentication certificates in Mozilla Firefox. Usable by Apache Tomcat. |
| PKCS #13 | – | Elliptic-curve cryptography Standard | (Apparently abandoned, only reference is a proposal from 1998.) |
| PKCS #14 | – | Pseudo-random Number Generation | (Apparently abandoned, no documents exist.) |
| PKCS #15 | 1.1 | Cryptographic Token Information Format Standard | Defines a standard allowing users of cryptographic tokens to identify themselves to applications, independent of the application's Cryptoki implementation (PKCS #11) or other API. RSA has relinquished IC-card-related parts of this standard to ISO/IEC 7816-15. |