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Showing content from https://libsodium.gitbook.io/doc/advanced/sha-2_hash_function below:

SHA-2 | Libsodium documentation

1. Advanced

The SHA-256 and SHA-512 functions are provided for interoperability with other applications. If you are looking for a generic hash function and not specifically SHA-2, using crypto_generichash() (BLAKE2b) might be a better choice.

These functions are also not suitable for hashing passwords or deriving keys from passwords. Use one of the password hashing APIs instead.

These functions are not keyed and are thus deterministic. In addition, the untruncated versions are vulnerable to length extension attacks.

A message can be hashed in a single pass, but a streaming API is also available to process a message as a sequence of multiple chunks.

#define MESSAGE ((const unsigned char *) "test")
#define MESSAGE_LEN 4

unsigned char out[crypto_hash_sha256_BYTES];

crypto_hash_sha256(out, MESSAGE, MESSAGE_LEN);

#define MESSAGE_PART1 \
    ((const unsigned char *) "Arbitrary data to hash")
#define MESSAGE_PART1_LEN 22

#define MESSAGE_PART2 \
    ((const unsigned char *) "is longer than expected")
#define MESSAGE_PART2_LEN 23

unsigned char out[crypto_hash_sha256_BYTES];
crypto_hash_sha256_state state;

crypto_hash_sha256_init(&state);

crypto_hash_sha256_update(&state, MESSAGE_PART1, MESSAGE_PART1_LEN);
crypto_hash_sha256_update(&state, MESSAGE_PART2, MESSAGE_PART2_LEN);

crypto_hash_sha256_final(&state, out);

Single-part:

int crypto_hash_sha256(unsigned char *out, const unsigned char *in,
                       unsigned long long inlen);

Multi-part:

int crypto_hash_sha256_init(crypto_hash_sha256_state *state);

int crypto_hash_sha256_update(crypto_hash_sha256_state *state,
                              const unsigned char *in,
                              unsigned long long inlen);

int crypto_hash_sha256_final(crypto_hash_sha256_state *state,
                             unsigned char *out);

Single-part:

int crypto_hash_sha512(unsigned char *out, const unsigned char *in,
                       unsigned long long inlen);

Multi-part:

int crypto_hash_sha512_init(crypto_hash_sha512_state *state);

int crypto_hash_sha512_update(crypto_hash_sha512_state *state,
                              const unsigned char *in,
                              unsigned long long inlen);

int crypto_hash_sha512_final(crypto_hash_sha512_state *state,
                             unsigned char *out);

The state must be initialized with crypto_hash_sha*_init() before updating or finalizing it.

After crypto_hash_sha*_final(), the state should not be used any more, unless it is reinitialized using crypto_hash_sha*_init().

SHA-512-256 is also available via the higher-level interface crypto_hash().

As an alternative to crypto_auth_hmac*() or crypto_generichash(), the SHA-256 and SHA-512 hash functions can be keyed , but the key must be placed after the message, after having padded the message to the block size (64 bytes for SHA-256, 128 bytes for SHA-512). Using the key as a prefix, rather than a suffix would allow for length extension attacks.

Last updated 5 months ago

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