# Module Digest.BLAKE256

    module BLAKE256: S

`BLAKE256` is the BLAKE2b hash function producing 256-bit (32-byte) digests. It is cryptographically secure, and the digests are large enough to thwart brute-force attacks.

- Since 5.2

    type t = string

The type of digests.

    val hash_length : int

The length of digests, in bytes.

    val compare : t -> t -> int

Compare two digests, with the same specification as `compare`.

    val equal : t -> t -> bool

Test two digests for equality.

    val string : string -> t

Return the digest of the given string.

    val bytes : bytes -> t

Return the digest of the given byte sequence.

    val substring : string -> int -> int -> t

`substring s ofs len` returns the digest of the substring of `s` starting at index `ofs` and containing `len` characters.

    val subbytes : bytes -> int -> int -> t

`subbytes s ofs len` returns the digest of the subsequence of `s` starting at index `ofs` and containing `len` bytes.

    val channel : in_channel -> int -> t

Read characters from the channel and return their digest. See `Digest.channel` for the full specification.

    val file : string -> t

Return the digest of the file whose name is given.

    val output : out_channel -> t -> unit

Write a digest on the given output channel.

    val input : in_channel -> t

Read a digest from the given input channel.

    val to_hex : t -> string

Return the printable hexadecimal representation of the given digest.

- Raises `Invalid_argument` if the length of the argument is not `hash_length`,

    val of_hex : string -> t

Convert a hexadecimal representation back into the corresponding digest.

- Raises `Invalid_argument` if the length of the argument is not `2 * hash_length`, or if the arguments contains non-hexadecimal characters.