# 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 algorithm used is MD5.

The MD5 hash function is not cryptographically secure. Hence, this module should not be used for security-sensitive applications. More recent, 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.