libsodium_crypto_kdf (libsodium v3.0.1)

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Derive many subkeys from a single keybytes/0 byte master key with the default construction, currently BLAKE2b.

Each subkey is identified by a 64-bit integer SubkeyId and a contextbytes/0 byte context, such as <<"Examples">>, which separates keys derived for different purposes. Subkeys are between bytes_min/0 and bytes_max/0 bytes long. This is not a password hash; use libsodium_crypto_pwhash to derive keys from passwords.

Key = libsodium_crypto_kdf:keygen(),
Subkey1 = libsodium_crypto_kdf:derive_from_key(32, 1, <<"Examples">>, Key),
Subkey2 = libsodium_crypto_kdf:derive_from_key(32, 2, <<"Examples">>, Key),
32 = byte_size(Subkey1),
true = Subkey1 =/= Subkey2,
Subkey1 = libsodium_crypto_kdf:derive_from_key(32, 1, <<"Examples">>, Key).

Summary

Types

ctx()

A crypto_kdf_CONTEXTBYTES (8-byte) binary.

k()

A crypto_kdf_KEYBYTES (32-byte) binary.

key()

A crypto_kdf_KEYBYTES (32-byte) binary.

Functions

bytes_max()

Return crypto_kdf_bytes_max(), in bytes.

bytes_min()

Return crypto_kdf_bytes_min(), in bytes.

contextbytes()

Return crypto_kdf_contextbytes(), in bytes.

derive_from_key(SubkeyLen, SubkeyId, Ctx, Key)

Derive the SubkeyLen byte subkey number SubkeyId for the contextbytes/0 byte context Ctx from the keybytes/0 byte master key Key.

keybytes()

Return crypto_kdf_keybytes(), in bytes.

keygen()

Generate a random keybytes/0 byte master key.

primitive()

Return crypto_kdf_primitive() as an atom.

Types

ctx()

-type ctx() :: <<_:64>>.

A crypto_kdf_CONTEXTBYTES (8-byte) binary.

k()

-type k() :: <<_:256>>.

A crypto_kdf_KEYBYTES (32-byte) binary.

key()

-type key() :: <<_:256>>.

A crypto_kdf_KEYBYTES (32-byte) binary.

Functions

bytes_max()

-spec bytes_max() -> Result when Result :: 64.

Return crypto_kdf_bytes_max(), in bytes.

bytes_min()

-spec bytes_min() -> Result when Result :: 16.

Return crypto_kdf_bytes_min(), in bytes.

contextbytes()

-spec contextbytes() -> Result when Result :: 8.

Return crypto_kdf_contextbytes(), in bytes.

derive_from_key(SubkeyLen, SubkeyId, Ctx, Key)

-spec derive_from_key(SubkeyLen, SubkeyId, Ctx, Key) -> Result
                         when
                             SubkeyLen :: non_neg_integer(),
                             SubkeyId :: non_neg_integer(),
                             Ctx :: ctx(),
                             Key :: key(),
                             Result :: binary() | -1.

Derive the SubkeyLen byte subkey number SubkeyId for the contextbytes/0 byte context Ctx from the keybytes/0 byte master key Key.

Returns -1 when SubkeyLen is outside bytes_min/0 to bytes_max/0.

keybytes()

-spec keybytes() -> Result when Result :: 32.

Return crypto_kdf_keybytes(), in bytes.

keygen()

-spec keygen() -> Result when Result :: k().

Generate a random keybytes/0 byte master key.

primitive()

-spec primitive() -> Result when Result :: blake2b.

Return crypto_kdf_primitive() as an atom.