# Secure Remote Storage of Logs with Search Capabilities
## 3 Related Work  
Securing logs is not a new concept since some work can even be found in a pre-cloud era. [PERSON] and [PERSON] [61] were the first to propose a solution to enhance the security of logs. The authors define a forward integrity security property and demonstrate its application to secure and verifiable logs. Key issues being intrusion detection, accountability and communications security. A forward secure stream integrity is presented and constructed by the use of a forward-secure MACs scheme, in which the log entries are indexed based on time periods. This solution enables a flow integrity of log entries. Based on this work, multiple research efforts appeared. [PERSON] and [PERSON] [62] proposed a protocol, using symmetric cryptographic, focused on the storage of audit logs. The scheme employs an one-way hash chain [63] used to create a dependency among the log entries. This dependency enables the detection of unauthorized modification in the log sequence since any alteration would break the consistency of the hash chain. An hash chain consists of a successive computation of cryptographic hash functions, where the input of the current hash also includes the output of the previous one. The authors also considered the use of evolving cryptography keys [64] to protect the audit trails and support computer forensics. Evolving cryptography can be seen as an encryption technique in which symmetric keys evolve over time, with the goal of limiting the impact of key compromise. Alongside the communication and storage overhead, since an authentication tag is generated and stored for each individual log entry, the scheme was proven to be vulnerable to truncation attacks. A truncation attack consists of the deletion of tail end log entries without being detected, thereby breaking the log entries integrity. In 2005, [PERSON] et al. proposed a generic secure logging solution [65] that makes use of covert channels for log transmission. It aims at addressing the lack of security of the syslog protocol [66] with problems related to the transmission of data, message integrity and message authenticity. A covert channel can be used in any communication channel to transmit information using methods not originally though of. The authors explored the possibility of transmitting log data using ordinary DNS requests and responses. They used DNS Security Extensions, asymmetric cryptography, and hash functions, such as the MD5 [67] and the SHA-1 [68] algorithms, considered safe at the time of their publication, to assure messages authenticity and integrity. [PERSON] et al. proposed Logcrypt [69], a secure logging protocol. Logs are initialized in a known state, stored on an external server, and the integrity of an earlier state can be used to verify the integrity of a later state. The solution provides two different approaches. The simpler one is based on MACs, in which an initial secret random value is used to initialize an hash chain. Each link of the hash chain is then used to derive secret keys for log data encryption. The use of symmetric encryption requires that any entity, who desires to verify the integrity of a log entry, must have the secret key used with the MAC function. Any entity that knows the key can forge log entries and, consequently, break the system's security. To address this problem, [PERSON] proposed the second approach that uses asymmetric encryption combined with identity-based signatures [70]. Replacing MACs with digital signatures enables the verification of log entries by any entity without disclosing private keys. While the use of asymmetric cryptography simplifies the log entry verification, it creates not only a communication overhead, originated from the constant key pair exchanges between the parties involved, but also a storage overhead since asymmetric key signatures are usually larger than MACs. [PERSON] et al. [71] proposed a new approach to secure logging.