CheckSignature

(Engine-Level Function)

Description:	Checks a digital signature with a key given a handle returned from Hash().
Returns:	Boolean
Usage:	Script Only.
Function Groups:	Cryptography
Related to:	GenerateSignature
Format:	CheckSignature(HashHandle, Signature, Key)
Parameters:

HashHandle

Required. Handle returned from a call to Hash()

Signature

Required text. The signature to be checked.

Key

Required handle to the public key, with which to check the signature. Previously obtained from any of GenerateKey(), ImportKey(), DeriveKey(). This must be an asymmetric public key

PaddingType

Optional integer. Can be one of the following values: Value~Meaning 0~No padding is to added to the plaintext data before signing. 1~Padding is added to the data before signing in accordance with the RSASSA-PKCS1-v1_5 scheme. 2~Padding is added to the data before signing in accordance with the RSASSA-PSS scheme.

PadHashAlgorithm

Optional text value. The algorithm to be used for padding the data. The hash is then signed.

SaltLength

Optional integer. Only required for RSASSA-PSS padding. This is the length of the salt used by that scheme.

Comments

none.

Example:

<
{============================ CheckSignatureSample ===========================}
{ Sample code using CheckSignature().                                         }
{=============================================================================}
CheckSignatureSample
(
  Message                     { Message to check                              };
  Signature                   { Signature for message                         };
  KeyBlob                     { Public key to check with                      };
)
[
  Protected Constant PROV_RSA_AES  = 24      { Enhanced RSA/AES provider      };
  Protected Constant KEY_SIZE      = 2048    { 2048 bit keys                  };
  Protected Constant PUBLICKEYBLOB = 6       { PUBLICKEYBLOB                  };
  Protected Constant CRYPT_VERIFYCONTEXT = 0xF0000000 { CRYPT_VERIFYCONTEXT   };

  Protected CSP               { Cryptographic context                         };
  Protected HashObj           { Intermediate handle returned from Hash()      };
  Protected Key               { Handle to signing key pair                    };
  Protected SignatureOK       { True if the signature is correct              };
]

Sign [
  If 1;
  [
    { Get cryptographic context }
    CSP = GetCryptoProvider(PROV_RSA_AES, Invalid, Invalid, CRYPT_VERIFYCONTEXT);

    { Import the public key }
    Key = ImportKey(CSP, PUBLICKEYBLOB, KeyBlob);

    { Compute a SHA-256 hash of the message }
    Hash(Message, 2 {SHA-256}, Invalid, HashObj, CSP);

    { Check signature }
    SignatureOK = CheckSignature(HashObj, Signature, Key);

    Return(SignatureOK);
  ]
]

{ End of CheckSignatureSample }
>