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Module Netauth

module Netauth: sig .. end
Some primitives for authentication

val hmac : h:(string -> string) ->
b:int -> l:int -> k:string -> message:string -> string
The HMAC algorithm of RFC 2104. The function h is the hash function. b and l are properties of h (see the RFC or below). The string k is the key, up to b bytes. The message is authenticated.

The key k should ideally have length l. If this cannot be ensured by other means, one should pass k = h any_k.

Common values of b and l:

  • For h=MD5: b=64, l=16
  • For h=SHA-1: b=64, l=20

type key_type = [ `Kc | `Ke | `Ki ] 
Key types:
  • `Kc is used for computing checksums
  • `Ke is used for encrypting confidential messages
  • `Ki is used for computing integrity checksums for encrypted messages

val derive_key_rfc3961_simplified : encrypt:(string -> string) ->
random_to_key:(string -> string) ->
block_size:int -> k:int -> usage:int -> key_type:key_type -> string
Derives a special key from a base key, as described in RFC 3961.

  • encrypt: Encrypts the argument with the base key and the initial cipher state.
  • random_to_key: Converts a random string of size k to a key
  • block_size: The block size of the cipher underlying encrypt. It is ensured that encrypt is called with strings having exactly this many bits. (The c parameter in the RFC text.) Minimum: 40.
  • k: The input size for random_to_key in bits. Must be divisible by 8.
  • usage: The usage number (here restricted to 0-255, although the RFC would allow 32 bits). Examples for usage numbers can be found in RFC 4121 section 2.
  • key_type: Which key type to derive
The output is a key as produced by random_to_key.

Bitstring operations

val xor_s : string -> string -> string
Performs the bitwise XOR of these strings (which must have the same length)
val add_1_complement : string -> string -> string
The addition algorithm for 1's-complement numbers. The two numbers to add are given as bitstrings (big endian), and must have the same length
val rotate_right : int -> string -> string
Rotate the (big-endian) bitstring to the right by n bits. This also works for negative n (left rotation), and for n whose absolute value is greater or equal than the bit length of the string.
val n_fold : int -> string -> string
Blumenthal's n-fold algorithm for an n that is divisible by 8. (RFC 3961, section 5.1)
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