Xojo Plugin

ECDSA Sign and Verify

See more ECC Examples

Demonstrates how to create an ECDSA signature on the SHA256 hash of some data, and then verify. Xojo Plugin

Dim success As Boolean
success = False

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

// First load an ECDSA private key to be used for signing.
Dim privKey As New Chilkat.PrivateKey
success = privKey.LoadEncryptedPemFile("qa_data/ecc/secp256r1-key-pkcs8-secret.pem","secret")
If (success = False) Then
    System.DebugLog(privKey.LastErrorText)
    Return
End If

// Sign the SHA256 hash of some data.
Dim bd As New Chilkat.BinData
success = bd.LoadFile("qa_data/hamlet.xml")
If (success = False) Then
    System.DebugLog("Failed to load file to be hashed.")
    Return
End If

Dim crypt As New Chilkat.Crypt2
crypt.HashAlgorithm = "sha256"
crypt.EncodingMode = "base64"
Dim hashStr As String
hashStr = crypt.HashBdENC(bd)

Dim ecdsa As New Chilkat.Ecc
Dim prng As New Chilkat.Prng
// Returns ASN.1 signature as a base64 string.
Dim sig As String
sig = ecdsa.SignHashENC(hashStr,"base64",privKey,prng)
System.DebugLog("sig = " + sig)

// The signature is in ASN.1 format (which may be described as the "encoded DSS signature").
// SEQUENCE (2 elem)
//   INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
//   INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...

// If you wish, you can get the r and s components of the signature like this:
Dim asn As New Chilkat.Asn
success = asn.LoadEncoded(sig,"base64")
Dim xml As New Chilkat.Xml
success = xml.LoadXml(asn.AsnToXml())

System.DebugLog(xml.GetXml())

// We now have this:
// <?xml version="1.0" encoding="utf-8"?>
// <sequence>
//     <int>6650D422D86BA4A228B5617604E59052591B9B2C32EF324C44D09EF67E5F0060</int>
//     <int>0CFD9F6AC85042FC70F672C141BA6B2A4CAFBB906C3D907BCCC1BED62B28326F</int>
// </sequence>

// Get the "r" and "s" as hex strings
Dim r As String
r = xml.GetChildContentByIndex(0)
Dim s As String
s = xml.GetChildContentByIndex(1)

System.DebugLog("r = " + r)
System.DebugLog("s = " + s)

// --------------------------------------------------------------------
// Now verify against the hash of the original data.

// Get the corresponding public key.
Dim pubKey As New Chilkat.PublicKey
success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pub.pem")
If (success = False) Then
    System.DebugLog(pubKey.LastErrorText)
    Return
End If

// We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
Dim ecc2 As New Chilkat.Ecc
Dim result As Int32
result = ecc2.VerifyHashENC(hashStr,sig,"base64",pubKey)
If (result <> 1) Then
    System.DebugLog(ecc2.LastErrorText)
    Return
End If

System.DebugLog("Verified!")

// Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
Dim xml2 As New Chilkat.Xml
xml2.Tag = "sequence"
xml2.NewChild2 "int",r
xml2.NewChild2 "int",s

Dim asn2 As New Chilkat.Asn
success = asn2.LoadAsnXml(xml2.GetXml())
Dim encodedSig As String
encodedSig = asn2.GetEncodedDer("base64")
System.DebugLog("encoded DSS signature: " + encodedSig)

// You can go to https://lapo.it/asn1js/  and copy/paste the base64 encodedSig into the online tool, then press the "decode" button.
// You will see the ASN.1 such as this:

// SEQUENCE (2 elem)
//   INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
//   INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...