(PureBasic) Verfies an RSA Signature

See more Apple Keychain Examples

Verifies an RSA signature against the original data.

Chilkat PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkBinData.pb"
IncludeFile "CkRsa.pb"
IncludeFile "CkPublicKey.pb"

Procedure ChilkatExample()

    ; The following data was signed by the following example:
    ; RSA Sign using a Private Key on a USB Token or Smartcard
    bd.i = CkBinData::ckCreate()
    If bd.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    i.i
    For i = 0 To 100
        CkBinData::ckAppendEncoded(bd,"000102030405060708090A0B0C0D0E0F","hex")
    Next

    ; Load the signature
    bdSig.i = CkBinData::ckCreate()
    If bdSig.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success.i = CkBinData::ckLoadFile(bdSig,"rsaSignatures/test1.sig")
    If success = 0
        Debug "Failed to load the RSA signature"
        CkBinData::ckDispose(bd)
        CkBinData::ckDispose(bdSig)
        ProcedureReturn
    EndIf

    ; Get the public key to be used for signature verification.
    pubKey.i = CkPublicKey::ckCreate()
    If pubKey.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkPublicKey::ckLoadFromFile(pubKey,"rsaKeys/chilkat-rsa-2048.pem")
    If success = 0
        Debug CkPublicKey::ckLastErrorText(pubKey)
        CkBinData::ckDispose(bd)
        CkBinData::ckDispose(bdSig)
        CkPublicKey::ckDispose(pubKey)
        ProcedureReturn
    EndIf

    rsa.i = CkRsa::ckCreate()
    If rsa.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkRsa::ckImportPublicKeyObj(rsa,pubKey)

    ; Verify the hash of the data against the signature.
    ; We pass in the original data.  Internally, the hash is generated
    ; and used to validate the signature.
    ; Validating the RSA signature means two things:  
    ; (1) the original data is exactly what was signed, and 
    ; (2) it was signed by the owner of the RSA private key.
    success = CkRsa::ckVerifyBd(rsa,bd,"sha256",bdSig)

    If success = 0
        Debug CkRsa::ckLastErrorText(rsa)
        Debug "Signature invalid."
    Else
        Debug "Signature valid."
    EndIf



    CkBinData::ckDispose(bd)
    CkBinData::ckDispose(bdSig)
    CkPublicKey::ckDispose(pubKey)
    CkRsa::ckDispose(rsa)


    ProcedureReturn
EndProcedure