High Efficiency Secure Channels for a Secure Multiparty Computation Protocol Based on Signal

Algorithm 1

: The pseudocode of the multireceiver sealed sender (from the rust library code of the Signal protocol).

	ENCRYPT(message, R_i):
	M = Random(32)
	r = KDF(label_r, M, len = 64)
	K = KDF(label_K, M, len = 32)
	E = DeriveKeyPair(r)
	for i in num_recipients:
	C_i = KDF(label_DH, DH(E, R_i) ||E.public ||R_i.public, len = 32) XOR M
	AT_i = KDF(label_DH_s, DH(S, R_i) ||E.public ||C_i ||S.public ||R_i.public, len = 16)
	ciphertext = AEAD_Encrypt(K, message)
	return E.public, C_i, AT_i, ciphertext
	DECRYPT(E.public, C, AT, ciphertext):
	M = KDF(label_DH, DH(E, R) ||E.public ||R.public, len = 32) xor C
	r = KDF(label_r, M, len = 64)
	K = KDF(label_K, M, len = 32)
	E′ = DeriveKeyPair(r)
	if E.public ! = E′.public:
	return DecryptionError
	message = AEAD_Decrypt(K, ciphertext)//includes S.public
	AT′ = KDF(label_DH_s, DH(S, R) ||E.public ||C ||S.public ||R.public, len = 16)
	if AT ! = AT′:
	return DecryptionError
	return message