Visual FoxPro

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. Visual FoxPro

LOCAL lnSuccess
LOCAL loCrypt
LOCAL lcHashStr
LOCAL loDsa
LOCAL lcPemPrivateKey
LOCAL lcAsnSig
LOCAL loAsn
LOCAL loXml
LOCAL r
LOCAL s
LOCAL loDsa2
LOCAL lcPemPublicKey

lnSuccess = 0

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

loCrypt = CreateObject('Chilkat.Crypt2')

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

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

loDsa = CreateObject('Chilkat.Dsa')

lcPemPrivateKey = loDsa.LoadText("qa_data/dsa/dsaPrivKey2.pem")
lnSuccess = loDsa.FromPem(lcPemPrivateKey)
IF (lnSuccess = 0) THEN
    ? loDsa.LastErrorText
    RELEASE loCrypt
    RELEASE loDsa
    CANCEL
ENDIF

* Load the hash to be signed into the DSA object:
lnSuccess = loDsa.SetEncodedHash("hex",lcHashStr)
IF (lnSuccess = 0) THEN
    ? loDsa.LastErrorText
    RELEASE loCrypt
    RELEASE loDsa
    CANCEL
ENDIF

* Sign the hash.
lnSuccess = loDsa.SignHash()
IF (lnSuccess = 0) THEN
    ? loDsa.LastErrorText
    RELEASE loCrypt
    RELEASE loDsa
    CANCEL
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('Chilkat.Asn')
lnSuccess = loAsn.LoadEncoded(lcAsnSig,"base64")
IF (lnSuccess = 0) THEN
    ? loAsn.LastErrorText
    RELEASE loCrypt
    RELEASE loDsa
    RELEASE loAsn
    CANCEL
ENDIF

* Get the ASN.1 as XML.
loXml = CreateObject('Chilkat.Xml')
lnSuccess = 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
lnSuccess = 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('Chilkat.Dsa')

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

lcPemPublicKey = loDsa2.LoadText("qa_data/dsa/dsaPubKey2.pem")
lnSuccess = loDsa2.FromPublicPem(lcPemPublicKey)
IF (lnSuccess = 0) THEN
    ? loDsa2.LastErrorText
    RELEASE loCrypt
    RELEASE loDsa
    RELEASE loAsn
    RELEASE loXml
    RELEASE loDsa2
    CANCEL
ENDIF

* Load the hash to be verified.
lnSuccess = loDsa2.SetEncodedHash("hex",lcHashStr)
IF (lnSuccess = 0) THEN
    ? loDsa2.LastErrorText
    RELEASE loCrypt
    RELEASE loDsa
    RELEASE loAsn
    RELEASE loXml
    RELEASE loDsa2
    CANCEL
ENDIF

* Load the ASN.1 signature:
lnSuccess = loDsa2.SetEncodedSignature("base64",lcAsnSig)
IF (lnSuccess = 0) THEN
    ? loDsa2.LastErrorText
    RELEASE loCrypt
    RELEASE loDsa
    RELEASE loAsn
    RELEASE loXml
    RELEASE loDsa2
    CANCEL
ENDIF

* Verify:
lnSuccess = loDsa2.Verify()
IF (lnSuccess = 0) THEN
    ? loDsa2.LastErrorText
ELSE
    ? "DSA Signature Verified!"
ENDIF

RELEASE loCrypt
RELEASE loDsa
RELEASE loAsn
RELEASE loXml
RELEASE loDsa2