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// Package message provides a structure for message keys, which are symmetric
// keys used for the encryption/decryption of Signal messages.
package message
// DerivedSecretsSize is the size of the derived secrets for message keys.
const DerivedSecretsSize = 80
// CipherKeyLength is the length of the actual cipher key used for messages.
const CipherKeyLength = 32
// MacKeyLength is the length of the message authentication code in bytes.
const MacKeyLength = 32
// IVLength is the length of the initialization vector in bytes.
const IVLength = 16
// KdfSalt is used as the Salt for message keys to derive secrets using a Key Derivation Function
const KdfSalt string = "WhisperMessageKeys"
// NewKeys returns a new message keys structure with the given cipherKey, mac, iv, and index.
func NewKeys(cipherKey, macKey, iv []byte, index uint32) *Keys {
messageKeys := Keys{
cipherKey: cipherKey,
macKey: macKey,
iv: iv,
index: index,
}
return &messageKeys
}
// NewKeysFromStruct will return a new message keys object from the
// given serializeable structure.
func NewKeysFromStruct(structure *KeysStructure) *Keys {
return NewKeys(
structure.CipherKey,
structure.MacKey,
structure.IV,
structure.Index,
)
}
// NewStructFromKeys returns a serializeable structure of message keys.
func NewStructFromKeys(keys *Keys) *KeysStructure {
return &KeysStructure{
CipherKey: keys.cipherKey,
MacKey: keys.macKey,
IV: keys.iv,
Index: keys.index,
}
}
// KeysStructure is a serializeable structure of message keys.
type KeysStructure struct {
CipherKey []byte
MacKey []byte
IV []byte
Index uint32
}
// Keys is a structure to hold all the keys for a single MessageKey, including the
// cipherKey, mac, iv, and index of the chain key. MessageKeys are used to
// encrypt individual messages.
type Keys struct {
cipherKey []byte
macKey []byte
iv []byte
index uint32
}
// CipherKey is the key used to produce ciphertext.
func (k *Keys) CipherKey() []byte {
return k.cipherKey
}
// MacKey returns the message's message authentication code.
func (k *Keys) MacKey() []byte {
return k.macKey
}
// Iv returns the message keys' initialization vector. The IV is a fixed-size input
// to a cryptographic primitive.
func (k *Keys) Iv() []byte {
return k.iv
}
// Index returns the number of times the chain key has been put through a key derivation
// function to generate this message key.
func (k *Keys) Index() uint32 {
return k.index
}
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