NaCl: Networking and Cryptography library

Computer Aided Cryptography Engineering

ECRYPT II

Public-key cryptography:

Authenticated encryption

Scalar multiplication

Signatures

Secret-key cryptography:

Authenticated encryption

Encryption

Authentication

One-time authentication

Low-level functions:

Hashing

String comparison

Hashing: crypto_hash

C++ interface

C++ NaCl provides a crypto_hash function callable as follows:

     #include "crypto_hash.h"

     std::string m;
     std::string h;

     h = crypto_hash(m);

The crypto_hash function hashes a message m. It returns a hash h. The output length h.size() is always crypto_hash_BYTES.

C interface

C NaCl provides a crypto_hash function callable as follows:

     #include "crypto_hash.h"

     const unsigned char m[...]; unsigned long long mlen;
     unsigned char h[crypto_hash_BYTES];

     crypto_hash(h,m,mlen);

The crypto_hash function hashes a message m[0], m[1], ..., m[mlen-1]. It puts the hash into h[0], h[1], ..., h[crypto_hash_BYTES-1]. It then returns 0.

Security model

The crypto_hash function is designed to be usable as a strong component of DSA, RSA-PSS, key derivation, hash-based message-authentication codes, hash-based ciphers, and various other common applications. "Strong" means that the security of these applications, when instantiated with crypto_hash, is the same as the security of the applications against generic attacks. In particular, the crypto_hash function is designed to make finding collisions difficult.

See Validation regarding safe message lengths.

Selected primitive

crypto_hash is currently an implementation of SHA-512.

There has been considerable degradation of public confidence in the security conjectures for many hash functions, including SHA-512. However, for the moment, there do not appear to be alternatives that inspire satisfactory levels of confidence. One can hope that NIST's SHA-3 competition will improve the situation.

Alternate primitives

NaCl supports the following hash functions:

`crypto_hash`	Primitive	`BYTES`
`crypto_hash_sha256`	SHA-256	32
`crypto_hash_sha512`	SHA-512	64

For example, a user who wants to hash with SHA-256 can simply replace crypto_hash, crypto_hash_BYTES, etc. with crypto_hash_sha256, crypto_hash_sha256_BYTES, etc.

Version

This is version 2019.03.19 of the hash.html web page.