Hpke.DerivePrivateKey Method

CryptoSys PKI Pro Manual

Hpke.DerivePrivateKey Method

Derive an EC private key in a deterministic manner from input keying material using the DeriveKeyPair algorithm in RFC9180.

Syntax

[C#]

public static string DerivePrivateKey(
   byte[] ikm,
   Hpke.CurveName curveName,
   Hpke.OutputOpts opts = Hpke.OutputOpts.Default 
)

[VB]

Public Shared Function DerivePrivateKey (
   ikm As Byte(),
   curveName As Hpke.CurveName,
   Optional opts As Hpke.OutputOpts = Hpke.OutputOpts.Default 
) As String

Parameters

ikm Byte: Input key material (ikm). This must have length in bytes at least as long as the key to be produced.
curveName Hpke.CurveName: Curve name
opts Hpke.OutputOpts (Optional): Output options (default=internal key format)

Return Value

String
Derived private key in string form or an empty string on error.

Remarks

By default the key is output as an ephemeral "internal" key string, which can be used directly with Ecc.SaveKey, Ecc.SaveEncKey, Ecc.PublicKeyFromPrivate, Ecc.DHSharedSecret and Ecc.QueryKey. If opts is set to `OutputOpts.KeyAsHex` then the key is output in serialized hexadecimal form in the same manner as the test vectors in [RFC9180] (without the clamping). The KDF to be used is fixed by the EC curve group as follows:

EC curve	KDF
P-256	HKDF-SHA256
P-384	HKDF-SHA384
P-521	HKDF-SHA512
X25519	HKDF-SHA256
X448	HKDF-SHA512

Example

string ikmhex = "7268600d403fce431561aef583ee1613527cff655c1343f29812e66706df3234";
string skhex = Hpke.DerivePrivateKey(Cnv.FromHex(ikmhex), Hpke.CurveName.X25519, Hpke.OutputOpts.KeyAsHex);
// 52c4a758a802cd8b936eceea314432798d5baf2d7e9235dc084ab1b9cfa2f736