AutoIt

ECDSA Sign Data and Get Raw R and S Values

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

Local $bSuccess = 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.

$oCrypt = ObjCreate("Chilkat.Crypt2")
$oCrypt.HashAlgorithm = "SHA256"
$oCrypt.Charset = "utf-8"
$oCrypt.EncodingMode = "base64"

; Hash a string.
Local $sHash1 = $oCrypt.HashStringENC("The quick brown fox jumps over the lazy dog")
ConsoleWrite("hash1 = " & $sHash1 & @CRLF)

; -----------------------------------------------------------
; 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-----

$oPrivKey = ObjCreate("Chilkat.PrivateKey")
$bSuccess = $oPrivKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
If ($bSuccess <> True) Then
    ConsoleWrite($oPrivKey.LastErrorText & @CRLF)
    Exit
EndIf

; Sign the hash..
$oPrng = ObjCreate("Chilkat.Prng")
$oEcdsa = ObjCreate("Chilkat.Ecc")
Local $sEcdsaSigBase64 = $oEcdsa.SignHashENC($sHash1,"base64",$oPrivKey,$oPrng)
If ($oEcdsa.LastMethodSuccess <> True) Then
    ConsoleWrite($oEcdsa.LastErrorText & @CRLF)
    Exit
EndIf

; 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

ConsoleWrite("Base64 ECDSA signature = " & $sEcdsaSigBase64 & @CRLF)

; If the raw R and S values are needed, here's how to get them:
$oAsn = ObjCreate("Chilkat.Asn")
$bSuccess = $oAsn.LoadEncoded($sEcdsaSigBase64,"base64")
If ($bSuccess = False) Then
    ConsoleWrite($oAsn.LastErrorText & @CRLF)
    Exit
EndIf

; The R and X will be in hexidecimal in the XML.
$oXml = ObjCreate("Chilkat.Xml")
$oXml.LoadXml($oAsn.AsnToXml())
ConsoleWrite($oXml.GetXml() & @CRLF)

; 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.
$oBd = ObjCreate("Chilkat.BinData")
Local $sR = $oXml.GetChildContent("int[0]")
Local $s = $oXml.GetChildContent("int[1]")
$oBd.AppendEncoded($sR,"hex")
$oBd.AppendEncoded($s,"hex")

ConsoleWrite("Number of bytes in bd: " & $oBd.NumBytes & @CRLF)