Module Stdlib.DigestSource

Message digest.

This module provides functions to compute 'digests', also known as 'hashes', of arbitrary-length strings or files. The supported hashing algorithms are BLAKE2 and MD5.

Basic functions

The functions in this section use the MD5 hash function to produce 128-bit digests (16 bytes). MD5 is not cryptographically secure. Hence, these functions should not be used for security-sensitive applications. The BLAKE2 functions below are cryptographically secure.

Sourcetype t = string

The type of digests: 16-byte strings.

Sourceval compare : t -> t -> int

The comparison function for 16-byte digests, with the same specification as Stdlib.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
Sourceval equal : t -> t -> bool

The equal function for 16-byte digests.

  • since 4.03
Sourceval string : string -> t

Return the digest of the given string.

Sourceval bytes : bytes -> t

Return the digest of the given byte sequence.

  • since 4.02
Sourceval 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.

Sourceval 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
Sourceval 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.

Sourceval file : string -> t

Return the digest of the file whose name is given.

Sourceval output : out_channel -> t -> unit

Write a digest on the given output channel.

Sourceval input : in_channel -> t

Read a digest from the given input channel.

Sourceval to_hex : t -> string

Return the printable hexadecimal representation of the given digest.

Sourceval of_hex : string -> t

Convert a hexadecimal representation back into the corresponding digest.

  • raises Invalid_argument

    if the argument is not exactly 32 hexadecimal characters.

  • since 5.2
Sourceval from_hex : string -> t

Same function as Digest.of_hex.

  • since 4.00

Generic interface

Sourcemodule type S = sig ... end

The signature for a hash function that produces digests of length hash_length from character strings, byte arrays, and files.

Specific hash functions

Sourcemodule BLAKE128 : S

BLAKE128 is the BLAKE2b hash function producing 128-bit (16-byte) digests. It is cryptographically secure. However, the small size of the digests enables brute-force attacks in 2{^64} attempts.

Sourcemodule 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.

Sourcemodule BLAKE512 : S

BLAKE512 is the BLAKE2b hash function producing 512-bit (64-byte) digests. It is cryptographically secure, and the digests are large enough to thwart brute-force attacks.

Sourcemodule MD5 : S

MD5 is the MD5 hash function. It produces 128-bit (16-byte) digests and is not cryptographically secure at all. It should be used only for compatibility with earlier designs that mandate the use of MD5.