B4X

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. B4X

Dim success As Boolean = 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 ChilkatCrypt2
crypt.Initialize("crypt")
crypt.HashAlgorithm = "SHA256"
crypt.Charset = "utf-8"
crypt.EncodingMode = "base64"

'  Hash a string.
Dim hash1 As String = crypt.HashStringENC("The quick brown fox jumps over the lazy dog")
Log("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 ChilkatPrivateKey
privKey.Initialize("privKey")
success = privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
If success <> True Then
    Log(privKey.LastErrorText)
    Return
End If


'  Sign the hash..
Dim prng As ChilkatPrng
prng.Initialize
Dim ecdsa As ChilkatEcc
ecdsa.Initialize
Dim ecdsaSigBase64 As String = ecdsa.SignHashENC(hash1, "base64", privKey, prng)
If ecdsa.LastMethodSuccess <> True Then
    Log(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

Log("Base64 ECDSA signature = " & ecdsaSigBase64)

'  If the raw R and S values are needed, here's how to get them:
Dim asn As ChilkatAsn
asn.Initialize
success = asn.LoadEncoded(ecdsaSigBase64, "base64")
If success = False Then
    Log(asn.LastErrorText)
    Return
End If


'  The R and X will be in hexidecimal in the XML.
Dim xml As ChilkatXml
xml.Initialize
xml.LoadXml(asn.AsnToXml)
Log(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 ChilkatBinData
bd.Initialize
Dim r As String = xml.GetChildContent("int[0]")
Dim s As String = xml.GetChildContent("int[1]")
bd.AppendEncoded(r, "hex")
bd.AppendEncoded(s, "hex")

Log("Number of bytes in bd: " & bd.NumBytes)