Using varbinary parameter with Dapper.NET

Question

I'm trying to use a varbinary parameter with Dapper.NET as follows

string secret = "secret";

// from SELECT ENCRYPTBYPASSPHRASE('secret', N'xx') >>;
string ciphertext = "0x01000000393FE233AE939CA815AB744DDC39667860B3B630C82F36F7"; 
using (var conn = new SqlConnection(...))
{
    var result = conn.ExecuteScalar(@"SELECT CONVERT(NVARCHAR(4000), DECRYPTBYPASSPHRASE(@secret, @ciphertext)) as decrypted", 
        new
        {
            secret,
            ciphertext = Encoding.Unicode.GetBytes(ciphertext)
        });
}

However the result is null. But it returns a valid result if I run the SQL directly eg.

SELECT CONVERT(NVARCHAR(40), DECRYPTBYPASSPHRASE('secret',  0x01000000393FE233AE939CA815AB744DDC39667860B3B630C82F36F7))

returns xx which is the encrypted text.

Any idea what I'm doing wrong?

`Encoding.Unicode.GetBytes` is going to get you the byte array of the *string representation* of your hex value — Rob, Oct 04 '16 at 03:53
Use [this](http://stackoverflow.com/questions/321370/how-can-i-convert-a-hex-string-to-a-byte-array) to get the correct value for `ciphertext` — Rob, Oct 04 '16 at 03:55

score 2 · Accepted Answer · answered Oct 10 '16 at 05:53

Just so someone finds useful, the following worked (Thanks @Rob for comments above)

public string Encrypt(string secret, string unprotectedText)
{
    using (var conn = new SqlConnection(...))
    {
        var x = conn.ExecuteScalar(@"SELECT ENCRYPTBYPASSPHRASE(@secret, @text)",
            new { secret, text });

        return ByteArrayToString((byte[])x);
    }
}

public string Decrypt(string secret, string ciphertext)
{
    using (var conn = new SqlConnection(...))
    {
        return conn.ExecuteScalar(@"SELECT CONVERT(NVARCHAR(4000), DECRYPTBYPASSPHRASE(@secret, @ciphertext))", 
            new { secret, ciphertext = StringToByteArray(ciphertext) }).ToString();
    }
}

and the hexstring-to-bytes and bytes-to-hexstring functions are

public static byte[] StringToByteArray(string hex)
{
    int startIndex = 0;
    if (hex.StartsWith("0x", StringComparison.InvariantCultureIgnoreCase))
        startIndex = 2;

    return Enumerable.Range(startIndex, hex.Length - startIndex)
                     .Where(x => x % 2 == 0)
                     .Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
                     .ToArray();
}

public static string ByteArrayToString(byte[] arr)
{
    return "0x" + BitConverter.ToString(arr).Replace("-", String.Empty);
}

Using varbinary parameter with Dapper.NET

1 Answers1