PHP's openssl_sign in C# using strings

Question

Is there an easy way to do this in C# ?

 openssl_sign($input, $output, $privateKey, OPENSSL_ALGO_SHA1)

$input is a string to be signed
$output - If the call was successful the signature is returned in this variable. It is a byte[]
$privateKey is a PEM private key (string)

Reference: http://php.net/manual/en/function.openssl-sign.php

I'm getting the input string from an XML, it is flattenned, like this:

<foo><bar1>qux1</bar1><bar2>qux2</bar2></foo>

I'm getting the privateKey string from the content of the <RSASK> tag in an XML:

<?xml version="1.0"?>
<bla1>foo</bla1>
<bla2>bar</bla2>
<RSASK>-----BEGIN RSA PRIVATE KEY-----
MIIBOgIBAAJBAMo8SSYPCvFBDgCqFv8o8UzznvcXO6FwUKmbDFogNIA5yQKTJc8i
VIYt6oXLfes+q5i+4oQWb6MJgTIZvcjmCL8CAQMCQQCG0ttutLH2K16rHA9UxfYz
TRSkuifA9YsbasdLmwCMAJVWbScsJcXdecXfWJJVcFTo5fFf6PIigPACHUZlSo8xb
AiEA9vjXy5u74OBS3ekQdMuKrUv5fi6z+EChhhCclVtFwhMCIQDRoMyppTxAmDDY
24QpFZQm9orgXgeqcg0vVoLCcaqUJQIhAKSl5TJn0pXq4elGCviHscjdUP7JzVAr
FuC1vbjng9a3AiEAi8CIcRjS1brLOz0Cxg5ixKRclZQFHEwIyjmsgaEcYsMCIEFT
oGduMC3vOMtKHEo8SAfDFeirfubo+FAZteQ0pyFF
-----END RSA PRIVATE KEY-----
</RSASK>

how is this "too broad"? it is NOT BROAD. There are 2 strings and an output byte[]. That is not broad. — sports
– sports, Commented Sep 5, 2018 at 19:29
You should take a look at this post: stackoverflow.com/questions/36931840/… — David Findley
– David Findley, Commented Sep 5, 2018 at 19:31

sports · Accepted Answer · 2018-09-07 20:00:47Z

It wasn't easy at all:

First, I needed to convert the input string to a byte[]

    ASCIIEncoding ByteConverter = new ASCIIEncoding();
    byte[] inputBytes = ByteConverter.GetBytes(input);

Compute its SHA1 Hash

    byte[] inputHash = new SHA1CryptoServiceProvider().ComputeHash(inputBytes);

Remove the beginning and end of the RSA PRIVATE KEY and convert it to byte[]

    byte[] privateKeyBytes = Convert.FromBase64String(privateKey
        .Replace("-----BEGIN RSA PRIVATE KEY-----", string.Empty)
        .Replace("-----END RSA PRIVATE KEY-----", string.Empty)
        .Replace("\n", string.Empty));

Then I had to create a RSACryptoServiceProvider from privateKeyBytes but I had to use a complicated class found on Internet:

    RSACryptoServiceProvider rsa = RSAUtils.DecodeRSAPrivateKey(privateKeyBytes);
                                   // ^
                                   // Found on Internet

Then I finally could sign

    byte[] output = rsa.SignHash(inputHash, "SHA1");

Code found on the Internet:

public class RSAUtils
{
    public static RSACryptoServiceProvider DecodeRSAPrivateKey(byte[] privkey)
    {
        byte[] MODULUS, E, D, P, Q, DP, DQ, IQ;

        // --------- Set up stream to decode the asn.1 encoded RSA private key ------
        MemoryStream mem = new MemoryStream(privkey);
        BinaryReader binr = new BinaryReader(mem);  //wrap Memory Stream with BinaryReader for easy reading
        byte bt = 0;
        ushort twobytes = 0;
        int elems = 0;
        try
        {
            twobytes = binr.ReadUInt16();
            if (twobytes == 0x8130) //data read as little endian order (actual data order for Sequence is 30 81)
                binr.ReadByte();    //advance 1 byte
            else if (twobytes == 0x8230)
                binr.ReadInt16();   //advance 2 bytes
            else
                return null;

            twobytes = binr.ReadUInt16();
            if (twobytes != 0x0102) //version number
                return null;
            bt = binr.ReadByte();
            if (bt != 0x00)
                return null;


            //------ all private key components are Integer sequences ----
            elems = GetIntegerSize(binr);
            MODULUS = binr.ReadBytes(elems);

            elems = GetIntegerSize(binr);
            E = binr.ReadBytes(elems);

            elems = GetIntegerSize(binr);
            D = binr.ReadBytes(elems);

            elems = GetIntegerSize(binr);
            P = binr.ReadBytes(elems);

            elems = GetIntegerSize(binr);
            Q = binr.ReadBytes(elems);

            elems = GetIntegerSize(binr);
            DP = binr.ReadBytes(elems);

            elems = GetIntegerSize(binr);
            DQ = binr.ReadBytes(elems);

            elems = GetIntegerSize(binr);
            IQ = binr.ReadBytes(elems);

            // ------- create RSACryptoServiceProvider instance and initialize with public key -----
            CspParameters CspParameters = new CspParameters();
            CspParameters.Flags = CspProviderFlags.UseMachineKeyStore;
            RSACryptoServiceProvider RSA = new RSACryptoServiceProvider(1024, CspParameters);
            RSAParameters RSAparams = new RSAParameters();
            RSAparams.Modulus = MODULUS;
            RSAparams.Exponent = E;
            RSAparams.D = D;
            RSAparams.P = P;
            RSAparams.Q = Q;
            RSAparams.DP = DP;
            RSAparams.DQ = DQ;
            RSAparams.InverseQ = IQ;
            RSA.ImportParameters(RSAparams);
            return RSA;
        }
        catch (Exception ex)
        {
            return null;
        }
        finally
        {
            binr.Close();
        }
    }

    private static int GetIntegerSize(BinaryReader binr)
    {
        byte bt = 0;
        byte lowbyte = 0x00;
        byte highbyte = 0x00;
        int count = 0;
        bt = binr.ReadByte();
        if (bt != 0x02)      //expect integer
            return 0;
        bt = binr.ReadByte();

        if (bt == 0x81)
            count = binr.ReadByte();    // data size in next byte
        else
            if (bt == 0x82)
            {
                highbyte = binr.ReadByte();    // data size in next 2 bytes
                lowbyte = binr.ReadByte();
                byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };
                count = BitConverter.ToInt32(modint, 0);
            }
            else
            {
                count = bt;      // we already have the data size
            }

        while (binr.ReadByte() == 0x00)
        {    //remove high order zeros in data
            count -= 1;
        }
        binr.BaseStream.Seek(-1, SeekOrigin.Current);        //last ReadByte wasn't a removed zero, so back up a byte
        return count;
    }

}

Testing that it works.

Php Test

$input = "<DD><RE>97975000-5</RE><TD>33</TD><F>27</F><FE>2003-09-08</FE><RR>8414240-9</RR><RSR>JORGE GONZALEZ LTDA</RSR><MNT>502946</MNT><IT1>Cajon AFECTO</IT1><CAF version=\"1.0\"><DA><RE>97975000-5</RE><RS>RUT DE PRUEBA</RS><TD>33</TD><RNG><D>1</D><H>200</H></RNG><FA>2003-09-04</FA><RSAPK><M>0a4O6Kbx8Qj3K4iWSP4w7KneZYeJ+g/prihYtIEolKt3cykSxl1zO8vSXu397QhTmsX7SBEudTUx++2zDXBhZw==</M><E>Aw==</E></RSAPK><IDK>100</IDK></DA><FRMA algoritmo=\"SHA1withRSA\">g1AQX0sy8NJugX52k2hTJEZAE9Cuul6pqYBdFxj1N17umW7zG/hAavCALKByHzdYAfZ3LhGTXCai5zNxOo4lDQ==</FRMA></CAF><TSTED>2003-09-08T12:28:31</TSTED></DD>";
$privateKey = "-----BEGIN RSA PRIVATE KEY-----\nMIIBOwIBAAJBANGuDuim8fEI9yuIlkj+MOyp3mWHifoP6a4oWLSBKJSrd3MpEsZdczvL0l7t/e0IU5rF+0gRLnU1Mfvtsw1wYWcCAQMCQQCLyV9FxKFLW09yWw7bVCCdxpRDr7FRX/EexZB4VhsNxm/vtJfDZyYle0Lfy42LlcsXxPm1w6Q6NnjuW+AeBy67AiEA7iMi5q5xjswqq+49RP55o//jqdZL/pC9rdnUKxsNRMMCIQDhaHdIctErN2hCIP9knS3+9zra4R+5jSXOvI+3xVhWjQIhAJ7CF0R0S7SIHHKe04NUURf/7RvkMqm108k74sdnXi3XAiEAlkWk2vc2HM+a1sCqQxNz/098ketqe7NuidMKeoOQObMCIQCkFAMS9IcPcMjk7zI2r/4EEW63PSXyN7MFAX7TYe25mw==\n-----END RSA PRIVATE KEY-----";
openssl_sign($input, $output, $privateKey, OPENSSL_ALGO_SHA1);
echo(base64_encode($output));

The PHP output is:

pqjXHHQLJmyFPMRvxScN7tYHvIsty0pqL2LLYaG43jMmnfiZfllLA0wb32lP+HBJ/tf8nziSeorvjlx410ZImw==

C# Test

string input = "<DD><RE>97975000-5</RE><TD>33</TD><F>27</F><FE>2003-09-08</FE><RR>8414240-9</RR><RSR>JORGE GONZALEZ LTDA</RSR><MNT>502946</MNT><IT1>Cajon AFECTO</IT1><CAF version=\"1.0\"><DA><RE>97975000-5</RE><RS>RUT DE PRUEBA</RS><TD>33</TD><RNG><D>1</D><H>200</H></RNG><FA>2003-09-04</FA><RSAPK><M>0a4O6Kbx8Qj3K4iWSP4w7KneZYeJ+g/prihYtIEolKt3cykSxl1zO8vSXu397QhTmsX7SBEudTUx++2zDXBhZw==</M><E>Aw==</E></RSAPK><IDK>100</IDK></DA><FRMA algoritmo=\"SHA1withRSA\">g1AQX0sy8NJugX52k2hTJEZAE9Cuul6pqYBdFxj1N17umW7zG/hAavCALKByHzdYAfZ3LhGTXCai5zNxOo4lDQ==</FRMA></CAF><TSTED>2003-09-08T12:28:31</TSTED></DD>";
string privateKey = "-----BEGIN RSA PRIVATE KEY-----\nMIIBOwIBAAJBANGuDuim8fEI9yuIlkj+MOyp3mWHifoP6a4oWLSBKJSrd3MpEsZdczvL0l7t/e0IU5rF+0gRLnU1Mfvtsw1wYWcCAQMCQQCLyV9FxKFLW09yWw7bVCCdxpRDr7FRX/EexZB4VhsNxm/vtJfDZyYle0Lfy42LlcsXxPm1w6Q6NnjuW+AeBy67AiEA7iMi5q5xjswqq+49RP55o//jqdZL/pC9rdnUKxsNRMMCIQDhaHdIctErN2hCIP9knS3+9zra4R+5jSXOvI+3xVhWjQIhAJ7CF0R0S7SIHHKe04NUURf/7RvkMqm108k74sdnXi3XAiEAlkWk2vc2HM+a1sCqQxNz/098ketqe7NuidMKeoOQObMCIQCkFAMS9IcPcMjk7zI2r/4EEW63PSXyN7MFAX7TYe25mw==\n-----END RSA PRIVATE KEY-----";

ASCIIEncoding ByteConverter = new ASCIIEncoding();
byte[] inputBytes = ByteConverter.GetBytes(input);

byte[] inputHash = new SHA1CryptoServiceProvider().ComputeHash(inputBytes);

byte[] privateKeyBytes = Convert.FromBase64String(privateKey
    .Replace("-----BEGIN RSA PRIVATE KEY-----", string.Empty)
    .Replace("-----END RSA PRIVATE KEY-----", string.Empty)
    .Replace("\n", string.Empty));

RSACryptoServiceProvider rsa = RSAUtils.DecodeRSAPrivateKey(privateKeyBytes);

byte[] output = rsa.SignHash(inputHash, "SHA1");

Console.WriteLine(Convert.ToBase64String(output));

The C# output is:

pqjXHHQLJmyFPMRvxScN7tYHvIsty0pqL2LLYaG43jMmnfiZfllLA0wb32lP+HBJ/tf8nziSeorvjlx410ZImw==

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