B4X Requires Chilkat v11.0.0+

RSA Signature/Verify with .key and .cer

See more RSA Examples

Demonstrates how to use a .key file (private key) and digital certificate (.cer, public key) to create and verify an RSA signature. B4X

Dim success As Boolean = False

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

Dim privKey As ChilkatPrivateKey
privKey.Initialize("privKey")

'  Load the private key from an RSA .key file:
success = privKey.LoadPemFile("privateKey.key")
If success = False Then
    Log(privKey.LastErrorText)
    Return
End If


Dim rsa As ChilkatRsa
rsa.Initialize

'  Import the private key into the RSA component:
success = rsa.UsePrivateKey(privKey)
If success = False Then
    Log(rsa.LastErrorText)
    Return
End If


'  Create the signature as a hex string:
rsa.EncodingMode = "hex"

Dim strData As String = "This is the string to be signed."

'  Sign the string using the sha256 hash algorithm.
'  Other valid choices are "md2", "sha1", "sha384",
'  "sha512", and "md5".
Dim hexSig As String = rsa.SignStringENC(strData, "sha256")

Log(hexSig)

'  Load a digital certificate from a .cer file:
Dim cert As ChilkatCert
cert.Initialize("cert")

success = cert.LoadFromFile("myCert.cer")
If success = False Then
    Log(cert.LastErrorText)
    Return
End If


Dim pubKey As ChilkatPublicKey
pubKey.Initialize
cert.GetPublicKey(pubKey)

'  Now verify using a new instance of the RSA object:
Dim rsa2 As ChilkatRsa
rsa2.Initialize

'  Import the public key into the RSA object:
success = rsa2.UsePublicKey(pubKey)
If success = False Then
    Log(rsa2.LastErrorText)
    Return
End If


'  The signature is a hex string, so make sure the EncodingMode is correct:
rsa2.EncodingMode = "hex"

'  Verify the signature:
success = rsa2.VerifyStringENC(strData, "sha256", hexSig)
If success = False Then
    Log(rsa2.LastErrorText)
    Return
End If


Log("Success.")