Lianja

DSA R,S Signature Values

See more DSA Examples

Creates a DSA signature. Gets r,s values from the signature. Re-creates the DSA signature ASN.1 from the r,s values. Then verifies the signature using the re-created ASN.1 DSA signature. Lianja

llSuccess = .F.

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

loCrypt = createobject("CkCrypt2")

loCrypt.EncodingMode = "hex"
loCrypt.HashAlgorithm = "sha-1"

lcHashStr = loCrypt.HashFileENC("qa_data/hamlet.xml")
? "hash to sign: " + lcHashStr

loDsa = createobject("CkDsa")

lcPemPrivateKey = loDsa.LoadText("qa_data/dsa/dsaPrivKey2.pem")
llSuccess = loDsa.FromPem(lcPemPrivateKey)
if (llSuccess = .F.) then
    ? loDsa.LastErrorText
    release loCrypt
    release loDsa
    return
endif

// Load the hash to be signed into the DSA object:
llSuccess = loDsa.SetEncodedHash("hex",lcHashStr)
if (llSuccess = .F.) then
    ? loDsa.LastErrorText
    release loCrypt
    release loDsa
    return
endif

// Sign the hash.
llSuccess = loDsa.SignHash()
if (llSuccess = .F.) then
    ? loDsa.LastErrorText
    release loCrypt
    release loDsa
    return
endif

// Get the ASN.1 signature.
lcAsnSig = loDsa.GetEncodedSignature("base64")
? "Signature: " + lcAsnSig

// Examine the details of the ASN.1 signature.
// We want to get the r,s values as hex strings..
loAsn = createobject("CkAsn")
llSuccess = loAsn.LoadEncoded(lcAsnSig,"base64")
if (llSuccess = .F.) then
    ? loAsn.LastErrorText
    release loCrypt
    release loDsa
    release loAsn
    return
endif

// Get the ASN.1 as XML.
loXml = createobject("CkXml")
llSuccess = loXml.LoadXml(loAsn.AsnToXml())
? "Signature as XML: "
? loXml.GetXml()

// Sample XML shown here.
// The r and s values are the two hex strings in the XML.

// <?xml version="1.0" encoding="utf-8"?>
// <sequence>
//     <int>2C187F3AB6E47A66497B86CE97BB39E2133810F5</int>
//     <int>588E53D3F7B69636B48FD7175E99A3961BD7D775</int>
// </sequence>

// Pretend we're starting with r,s
r = "2C187F3AB6E47A66497B86CE97BB39E2133810F5"
s = "588E53D3F7B69636B48FD7175E99A3961BD7D775"

// Build the XML that will be converted to ASN.1
loXml.Clear()
loXml.Tag = "sequence"
loXml.NewChild2("int",r)
loXml.NewChild2("int",s)

// Convert the XML to ASN.1
llSuccess = loAsn.LoadAsnXml(loXml.GetXml())

// Emit the signature as DER encoded ASN.1 (base64)
lcAsnSig = loAsn.GetEncodedDer("base64")

// --------------------------------------------------------------------
// Verify the signature using the asnSig we built from the r,s values
// --------------------------------------------------------------------

loDsa2 = createobject("CkDsa")

// Load the DSA public key to be used for verification:

lcPemPublicKey = loDsa2.LoadText("qa_data/dsa/dsaPubKey2.pem")
llSuccess = loDsa2.FromPublicPem(lcPemPublicKey)
if (llSuccess = .F.) then
    ? loDsa2.LastErrorText
    release loCrypt
    release loDsa
    release loAsn
    release loXml
    release loDsa2
    return
endif

// Load the hash to be verified.
llSuccess = loDsa2.SetEncodedHash("hex",lcHashStr)
if (llSuccess = .F.) then
    ? loDsa2.LastErrorText
    release loCrypt
    release loDsa
    release loAsn
    release loXml
    release loDsa2
    return
endif

// Load the ASN.1 signature:
llSuccess = loDsa2.SetEncodedSignature("base64",lcAsnSig)
if (llSuccess = .F.) then
    ? loDsa2.LastErrorText
    release loCrypt
    release loDsa
    release loAsn
    release loXml
    release loDsa2
    return
endif

// Verify:
llSuccess = loDsa2.Verify()
if (llSuccess = .F.) then
    ? loDsa2.LastErrorText
else
    ? "DSA Signature Verified!"
endif



release loCrypt
release loDsa
release loAsn
release loXml
release loDsa2