Botan.Low.KDF

Key derivation functions are used to turn some amount of shared secret material into uniform random keys suitable for use with symmetric algorithms. An example of an input which is useful for a KDF is a shared secret created using Diffie-Hellman key agreement.

Typically a KDF is also used with a salt and a label. The salt should be some random information which is available to all of the parties that would need to use the KDF; this could be performed by setting the salt to some kind of session identifier, or by having one of the parties generate a random salt and including it in a message.

The label is used to bind the KDF output to some specific context. For instance if you were using the KDF to derive a specific key referred to as the “message key” in the protocol description, you might use a label of “FooProtocol v2 MessageKey”. This labeling ensures that if you accidentally use the same input key and salt in some other context, you still use different keys in the two contexts.

Key derivation function

type KDFName = ByteString

kdf

Arguments

:: KDFName

kdf_algo: KDF algorithm, e.g., "SP800-56C"

-> Int

out_len: the desired output length in bytes

-> ByteString

secret[]: the secret input

-> ByteString

salt[]: a diversifier

-> ByteString

label[]: purpose for the derived keying material

-> IO ByteString

out[]: buffer holding the derived key

KDF algorithms

pattern HKDF :: KDFName

hkdf :: HashName -> KDFName

pattern HKDF_Extract :: KDFName

hkdf_extract :: KDFName -> KDFName

pattern HKDF_Expand :: KDFName

hkdf_expand :: KDFName -> KDFName

pattern KDF2 :: KDFName

kdf2 :: KDFName -> KDFName

pattern KDF1_18033 :: KDFName

kdf1_18033 :: KDFName -> KDFName

pattern KDF1 :: KDFName

kdf1 :: KDFName -> KDFName

pattern TLS_12_PRF :: KDFName

tls_12_prf :: KDFName -> KDFName

pattern X9_42_PRF :: KDFName

x9_42_prf :: KDFName -> KDFName

pattern SP800_108_Counter :: KDFName

sp800_108_counter :: KDFName -> KDFName

pattern SP800_108_Feedback :: KDFName

sp800_108_feedback :: KDFName -> KDFName

pattern SP800_108_Pipeline :: KDFName

sp800_108_pipeline :: KDFName -> KDFName

pattern SP800_56A :: KDFName

sp800_56A :: KDFName -> KDFName

pattern SP800_56C :: KDFName

sp800_56C :: KDFName -> KDFName

Convenience

kdfs :: [KDFName]