Click or drag to resize

HpkeLabeledExpand Method

Compute the output of the LabeledExpand function as defined in RFC9180.

Namespace: CryptoSysPKI
Assembly: diCrSysPKINet (in diCrSysPKINet.dll) Version: 23.0.0.30549 (23.1.0.0)
Syntax
Copy
public static byte[] LabeledExpand(
	int numBytes,
	byte[] prk,
	string label,
	byte[] info,
	HpkeCurveName curveName,
	HpkeAeadAlg aeadAlg = HpkeAeadAlg.None
)

Parameters

numBytes  Int32
Required number of bytes (L) of output keying material.
prk  Byte
Pseudorandom key (prk)
label  String
Label string
info  Byte
Byte string info
curveName  HpkeCurveName
ECDH curve used in scheme
aeadAlg  HpkeAeadAlg  (Optional)
AEAD encryption algorithm used in the scheme or 0 (default) to indicate KDF is being used inside a KEM algorithm.

Return Value

Byte
L bytes of output keying material.
Remarks
The LabeledExpand function is defined in section 4 of [RFC9180]. It uses the "expand" stage of the HKDF function [RFC5869]. The ECDH curve group used in the scheme must be specified, which automatically fixes the KDF and associated HMAC algorithm to be used.
Example
C#
Copy
int Nk = 16;
// key = LabeledExpand(secret, 'key', key_schedule_context, Nk)
byte[] key = Hpke.LabeledExpand(Nk, Cnv.FromHex("12fff91991e93b48de37e7daddb52981084bd8aa64289c3788471d9a9712f397"), "key",
   Cnv.FromHex("00725611c9d98c07c03f60095cd32d400d8347d45ed67097bbad50fc56da742d07cb6cffde367bb0565ba28bb02c90744a20f5ef37f30523526106f637abb05449"),
   Hpke.CurveName.X25519, Hpke.AeadAlg.Aes_128_Gcm);
// 4531685d41d65f03dc48f6b8302c05b0
See Also