# Module Digest

    module Digest: sig .. end

MD5 message digest.

This module provides functions to compute 128-bit 'digests' of arbitrary-length strings or files. The digests are of cryptographic quality: it is very hard, given a digest, to forge a string having that digest. The algorithm used is MD5. This module should not be used for secure and sensitive cryptographic applications. For these kind of applications more recent and stronger cryptographic primitives should be used instead.

    type t = string

The type of digests: 16-character strings.

    val compare : t -> t -> int

The comparison function for 16-character digest, with the same specification as `compare` and the implementation shared with `String.compare`. Along with the type `t`, this function `compare` allows the module `Digest` to be passed as argument to the functors `Set.Make` and `Map.Make`.

- Since 4.00.0

    val equal : t -> t -> bool

The equal function for 16-character digest.

- Since 4.03.0

    val string : string -> t

Return the digest of the given string.

    val bytes : bytes -> t

Return the digest of the given byte sequence.

- Since 4.02.0

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

`Digest.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

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

- Since 4.02.0

    val channel : in_channel -> int -> t

If `len` is nonnegative, `Digest.channel ic len` reads `len` characters from channel `ic` and returns their digest, or raises `End_of_file` if end-of-file is reached before `len` characters are read. If `len` is negative, `Digest.channel ic len` reads all characters from `ic` until end-of-file is reached and return their digest.

    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 argument is not exactly 16 bytes.

    val from_hex : string -> t

Convert a hexadecimal representation back into the corresponding digest.

- Since 4.00.0
- Raises `Invalid_argument` if the argument is not exactly 32 hexadecimal characters.