||FreeBSD Miscellaneous Information Manual
The in-kernel OpenCrypto framework supports several different encryption and
authentication algorithms. This document describes the parameters and
requirements of these algorithms. Unless otherwise noted, all sizes listed
below are in bytes.
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 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
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_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.
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.
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.
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
The following AEAD algorithms are supported:
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