Xojo Plugin

ECDSA Sign Data and Get Raw R and S Values

See more ECC Examples

Demonstrates getting the raw R and S value of an ECDSA signature. Xojo Plugin

Dim success As Boolean
success = False

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// To create an ECDSA signature, the data first needs to be hashed.  Then the hash
// is signed.

Dim crypt As New Chilkat.Crypt2
crypt.HashAlgorithm = "SHA256"
crypt.Charset = "utf-8"
crypt.EncodingMode = "base64"

// Hash a string.
Dim hash1 As String
hash1 = crypt.HashStringENC("The quick brown fox jumps over the lazy dog")
System.DebugLog("hash1 = " + hash1)

// -----------------------------------------------------------
// An ECDSA private key is used for signing.  The public key is for signature verification.
// Load our ECC private key.
// Our private key file contains this:

// 	// -----BEGIN PRIVATE KEY-----
// 	MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQg3J8q/24D1sEKGdP9
// 	72MGYElLGpw/a56Y3t6pfON3uhShRANCAATlSmoizyhAwoYZAOuFBATl07/1RR54
// 	a1Dzfm16grxJe666AGKR+bSs24hk7TEpaeCTvT8YOOM3l+xKFg7zq6Q9
// 	-----END PRIVATE KEY-----

Dim privKey As New Chilkat.PrivateKey
success = privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
If (success <> True) Then
    System.DebugLog(privKey.LastErrorText)
    Return
End If

// Sign the hash..
Dim prng As New Chilkat.Prng
Dim ecdsa As New Chilkat.Ecc
Dim ecdsaSigBase64 As String
ecdsaSigBase64 = ecdsa.SignHashENC(hash1,"base64",privKey,prng)
If (ecdsa.LastMethodSuccess <> True) Then
    System.DebugLog(ecdsa.LastErrorText)
    Return
End If

// The ECDSA signature is ASN.1 that contains a sequence of 2 large integers (r and s)
// For example:
// SEQUENCE (2 elem)
//   INTEGER (255 bit) 792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9
//   INTEGER (255 bit) 481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5

System.DebugLog("Base64 ECDSA signature = " + ecdsaSigBase64)

// If the raw R and S values are needed, here's how to get them:
Dim asn As New Chilkat.Asn
success = asn.LoadEncoded(ecdsaSigBase64,"base64")
If (success = False) Then
    System.DebugLog(asn.LastErrorText)
    Return
End If

// The R and X will be in hexidecimal in the XML.
Dim xml As New Chilkat.Xml
success = xml.LoadXml(asn.AsnToXml())
System.DebugLog(xml.GetXml())

// The XML looks like this:
// <sequence>
// <int>792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9</int>
// <int>481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5</int>
// </sequence>

// Copy raw R and S hex values into a Chilkat BinData object.
Dim bd As New Chilkat.BinData
Dim r As String
r = xml.GetChildContent("int[0]")
Dim s As String
s = xml.GetChildContent("int[1]")
success = bd.AppendEncoded(r,"hex")
success = bd.AppendEncoded(s,"hex")

System.DebugLog("Number of bytes in bd: " + Str(bd.NumBytes))