(SQL Server) Verify an RSA Signature Against the Signed String

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Demonstrates how to validate an RSA Signature against the string that was signed.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

-- Important: See this note about string length limitations for strings returned by sp_OAMethod calls.
--
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    -- Important: Do not use nvarchar(max).  See the warning about using nvarchar(max).
    DECLARE @sTmp0 nvarchar(4000)
    -- Create the same string we previously signed in this example: 
    -- RSA Sign utf-8 Bytes of String to get Base64 RSA Signature

    DECLARE @sb int
    -- Use "Chilkat_9_5_0.StringBuilder" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.StringBuilder', @sb OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    DECLARE @crlfLineEnding int
    SELECT @crlfLineEnding = 1
    DECLARE @i int

    SELECT @i = 0
    WHILE @i <= 10
      BEGIN
        DECLARE @success int
        EXEC sp_OAMethod @sb, 'AppendLine', @success OUT, 'This is a test.', @crlfLineEnding
        SELECT @i = @i + 1
      END

    DECLARE @base64_rsa_sig nvarchar(4000)
    SELECT @base64_rsa_sig = 'gWgpEXQqvXN6wh0MuFXPiw2xCb8cnmdizBT1TD1Tpm2GlJ8gnD59DGSj35GGXk1tM+mCOvMa2uW/9gmz8p6A90JLbn918i/2wKGvcde4wXnzPO7JADSNn2UwYzf3rp4/q/JrHv1GZETRJhABSFqTxOgdmdbEJQE/zijOSctCtQAM2CTb6t2BO8uHKSSUAwPH2cbeWxqsaVRLT4ruk5nZOxhoLgLMSjupiSzbE8zSTkkFOEHD+Mbb2xwg85AI0E4DsUnp+hLwwtS0blesgSyvtBY8oJODJeFcJsR7JDOTPdzHQHgJRl/2A4ij5xT91TpXy7ok43jhT6O9j7Q3qrafIQ=='

    -- Get the public key to be used for signature verification.
    DECLARE @pubKey int
    -- Use "Chilkat_9_5_0.PublicKey" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.PublicKey', @pubKey OUT

    DECLARE @success int
    EXEC sp_OAMethod @pubKey, 'LoadFromFile', @success OUT, 'rsaKeys/chilkat-rsa-2048.pem'
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @pubKey, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @sb
        EXEC @hr = sp_OADestroy @pubKey
        RETURN
      END

    DECLARE @rsa int
    -- Use "Chilkat_9_5_0.Rsa" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.Rsa', @rsa OUT

    EXEC sp_OAMethod @rsa, 'ImportPublicKeyObj', @success OUT, @pubKey

    -- Verify the string against the signature.
    -- We signed the utf-8 byte representation of the string, so we must indicate
    -- to also validate against the utf-8 byte representation.
    EXEC sp_OASetProperty @rsa, 'Charset', 'utf-8'
    EXEC sp_OASetProperty @rsa, 'EncodingMode', 'base64'
    DECLARE @signedString nvarchar(4000)
    EXEC sp_OAMethod @sb, 'GetAsString', @signedString OUT
    EXEC sp_OAMethod @rsa, 'VerifyStringENC', @success OUT, @signedString, 'sha256', @base64_rsa_sig

    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @rsa, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0

        PRINT 'Signature invalid.'
      END
    ELSE
      BEGIN

        PRINT 'Signature valid.'
      END

    EXEC @hr = sp_OADestroy @sb
    EXEC @hr = sp_OADestroy @pubKey
    EXEC @hr = sp_OADestroy @rsa


END
GO