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package ratchet
import (
"go.mau.fi/libsignal/kdf"
"go.mau.fi/libsignal/util/bytehelper"
)
// KdfInfo is optional bytes to include in deriving secrets with KDF.
const KdfInfo string = "WhisperGroup"
// NewSenderMessageKey will return a new sender message key using the given
// iteration and seed.
func NewSenderMessageKey(iteration uint32, seed []byte) (*SenderMessageKey, error) {
derivative, err := kdf.DeriveSecrets(seed, nil, []byte(KdfInfo), 48)
if err != nil {
return nil, err
}
// Split our derived secrets into 2 parts
parts := bytehelper.Split(derivative, 16, 32)
// Build the message key.
senderKeyMessage := &SenderMessageKey{
iteration: iteration,
seed: seed,
iv: parts[0],
cipherKey: parts[1],
}
return senderKeyMessage, nil
}
// NewSenderMessageKeyFromStruct will return a new message key object from the
// given serializeable structure.
func NewSenderMessageKeyFromStruct(structure *SenderMessageKeyStructure) *SenderMessageKey {
return &SenderMessageKey{
iteration: structure.Iteration,
iv: structure.IV,
cipherKey: structure.CipherKey,
seed: structure.Seed,
}
}
// NewStructFromSenderMessageKey returns a serializeable structure of message keys.
func NewStructFromSenderMessageKey(key *SenderMessageKey) *SenderMessageKeyStructure {
return &SenderMessageKeyStructure{
CipherKey: key.cipherKey,
Iteration: key.iteration,
IV: key.iv,
Seed: key.seed,
}
}
// SenderMessageKeyStructure is a serializeable structure of SenderMessageKeys.
type SenderMessageKeyStructure struct {
Iteration uint32
IV []byte
CipherKey []byte
Seed []byte
}
// SenderMessageKey is a structure for sender message keys used in group
// messaging.
type SenderMessageKey struct {
iteration uint32
iv []byte
cipherKey []byte
seed []byte
}
// Iteration will return the sender message key's iteration.
func (k *SenderMessageKey) Iteration() uint32 {
return k.iteration
}
// Iv will return the sender message key's initialization vector.
func (k *SenderMessageKey) Iv() []byte {
return k.iv
}
// CipherKey will return the key in bytes.
func (k *SenderMessageKey) CipherKey() []byte {
return k.cipherKey
}
// Seed will return the sender message key's seed.
func (k *SenderMessageKey) Seed() []byte {
return k.seed
}
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