crypto(7)

Authenticators

Authenticators compute a value (also known as a digest, hash, or tag) over an input of bytes. In-kernel requests can either compute the value for a given input, or verify if a given tag matches the computed tag for a given input. The following authentication algorithms are supported:

Block Ciphers

Block ciphers in OCF can only operate on messages whose length is an exact multiple of the cipher's block size. OCF supports the following block ciphers:

CRYPTO_AES_XTS implements XEX Tweakable Block Cipher with Ciphertext Stealing as defined in NIST SP 800-38E. OCF consumers provide the first 8 bytes of the IV. The remaining 8 bytes are defined to be a block counter beginning at 0.

NOTE: The ciphertext stealing part is not implemented in all backends which is why this cipher requires input that is a multiple of the block size.

Stream Ciphers

Stream ciphers can operate on messages with arbitrary lengths. OCF supports the following stream ciphers:

The IV for each request must be provided in crp_iv via the CRYPTO_F_IV_SEPARATE flag.

CRYPTO_AES_ICM uses the entire IV as a 128-bit big endian block counter. The IV sets the initial counter value for a message. If a consumer wishes to use an IV whose value is split into separate nonce and counter fields (e.g., IPsec), the consumer is responsible for splitting requests to handle counter rollover.

CRYPTO_CHACHA20 accepts a 16 byte IV. The first 8 bytes are used as a nonce. The last 8 bytes are used as a 64-bit little-endian block counter.

Authenticated Encryption with Associated Data Algorithms

AEAD algorithms in OCF combine a stream cipher with an authentication algorithm to provide both secrecy and authentication. AEAD algorithms accept additional authentication data (AAD) in addition to the ciphertext or plaintext. AAD is passed to the authentication algorithm as input in a method defined by the specific AEAD algorithm.

AEAD algorithms in OCF accept a nonce that is combined with an algorithm-defined counter to construct the IV for the underlying stream cipher. This nonce must be provided in crp_iv via the CRYPTO_F_IV_SEPARATE flag. Some AEAD algorithms support multiple nonce sizes. The first size listed is the default nonce size.

The following AEAD algorithms are supported: