Digest

Standard library namespace · Always available, with no import

A digest is a short fingerprint of some data. The same data always gives the same digest, and the smallest change to it gives a completely different one, so comparing digests is a quick way to check that a file or message has not changed. Digest makes two kinds: SHA-256, and HMAC-SHA256, which also uses a secret key.

const fingerprint = Digest.sha256("abc".to_bytes())
print(fingerprint.count)
print(fingerprint.to_hex())

Output

32
ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad

A digest is Bytes, 32 of them. To show or compare one the usual way, as hexadecimal text, use to_hex().

These digests never change between versions or computers, so they are safe to save and to compare later. That is different from a value’s own hash, used by dictionaries and sets, which is an internal detail and must not be saved.

Neither function is a way to store passwords. Storing passwords needs a scheme made for the job, which is not part of this library.

At a glance

Digests
Digest.sha256(bytes)	The SHA-256 digest of some bytes
Digest.hmac_sha256(bytes, key)	The HMAC-SHA256 digest of some bytes with a key

Digests

Digest.sha256(bytes: Bytes): Bytes

The 32-byte SHA-256 digest of bytes. To take the digest of text, turn it into bytes first with to_bytes().

print(Digest.sha256("".to_bytes()).to_hex())

Output

e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855

To check a file, read its bytes with File.read_binary and take their digest.

Digest.hmac_sha256(bytes: Bytes, key: Bytes): Bytes

The 32-byte HMAC-SHA256 digest of bytes, made with a secret key. Only someone who knows the key can make the digest for a given message, so it shows both that the message is unchanged and that it came from someone with the key. Web services often use it to sign what they send.

const message = "what do ya want for nothing?".to_bytes()
const key = "Jefe".to_bytes()
print(Digest.hmac_sha256(message, key).to_hex())

Output

5bdcc146bf60754e6a042426089575c75a003f089d2739839dec58b964ec3843