Added handling of Z85 encoding.

src/NetMQ.Tests/NetMQCertificateTest.cs

@@ -0,0 +1,25 @@
+using Xunit;
+
+namespace NetMQ.Tests
+{
+    public class NetMQCertificateTest : IClassFixture<CleanupAfterFixture>
+    {
+        public NetMQCertificateTest() => NetMQConfig.Cleanup();
+
+        [Fact]
+        public void X85()
+        {
+            for (int i = 0; i < 1000; i++)
+            {
+                var key = new NetMQCertificate();
+                var copy  = new NetMQCertificate(key.SecretKeyX85, key.PublicKeyX85);
+
+                Assert.Equal(key.SecretKeyX85, copy.SecretKeyX85);
+                Assert.Equal(key.PublicKeyX85, copy.PublicKeyX85);
+
+                Assert.Equal(key.SecretKey, copy.SecretKey);
+                Assert.Equal(key.PublicKey, copy.PublicKey);
+            }
+        }
+    }
+}

src/NetMQ/NetMQCertificate.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Collections.Generic;
+using System.Linq;
 using NaCl;
 
 namespace NetMQ
@@ -8,6 +10,115 @@ namespace NetMQ
     /// </summary>
     public class NetMQCertificate
     {
+        //  Z85 codec, taken from 0MQ RFC project, implements RFC32 Z85 encoding
+
+        //  Maps base 256 to base 85
+        private static string Encoder = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ.-:+=^!/*?&<>()[]{}@%$#";
+
+        //  Maps base 85 to base 256
+        //  We chop off lower 32 and higher 128 ranges
+        //  0xFF denotes invalid characters within this range
+        private static byte[] Decoder = {
+          0xFF, 0x44, 0xFF, 0x54, 0x53, 0x52, 0x48, 0xFF, 0x4B, 0x4C, 0x46, 0x41,
+          0xFF, 0x3F, 0x3E, 0x45, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+          0x08, 0x09, 0x40, 0xFF, 0x49, 0x42, 0x4A, 0x47, 0x51, 0x24, 0x25, 0x26,
+          0x27, 0x28, 0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E, 0x2F, 0x30, 0x31, 0x32,
+          0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x3B, 0x3C, 0x3D, 0x4D,
+          0xFF, 0x4E, 0x43, 0xFF, 0xFF, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10,
+          0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C,
+          0x1D, 0x1E, 0x1F, 0x20, 0x21, 0x22, 0x23, 0x4F, 0xFF, 0x50, 0xFF, 0xFF};
+
+        //  --------------------------------------------------------------------------
+        //  Encode a binary frame as a string; destination string MUST be at least
+        //  size * 5 / 4 bytes long plus 1 byte for the null terminator. Returns
+        //  dest. Size must be a multiple of 4.
+        //  Returns NULL for invalid input.
+        private string Z85Encode(byte[] data)
+        {
+            if (data.Length % 4 != 0) 
+            {
+                return null;
+            }
+
+            byte byte_nbr = 0;
+            UInt32 value = 0;
+            string dest = null;
+            while (byte_nbr<data.Length) {
+                //  Accumulate value in base 256 (binary)
+                value = value* 256 + data[byte_nbr++];
+                if (byte_nbr % 4 == 0) 
+                {
+                    //  Output value in base 85
+                    UInt32 divisor = 85 * 85 * 85 * 85;
+                    while (divisor != 0) 
+                    {
+                        dest += Encoder[(int)(value / divisor % 85)];
+                        divisor /= 85;
+                    }
+                    value = 0;
+                }
+            }
+
+            dest += char.MinValue;
+            return dest;
+        }
+
+
+        //  --------------------------------------------------------------------------
+        //  Decode an encoded string into a binary frame; dest must be at least
+        //  strlen (string) * 4 / 5 bytes long. Returns dest. strlen (string)
+        //  must be a multiple of 5.
+        //  Returns NULL for invalid input.
+        byte[] Z85Decode(string key)
+        {
+            UInt32 byte_nbr = 0;
+            UInt32 char_nbr = 0;
+            UInt32 value = 0;
+            var dest_ = new List<byte>();
+            foreach (var cha in key.TakeWhile(c => c != char.MinValue))
+            {
+
+                //  Accumulate value in base 85
+                if (UInt32.MaxValue / 85 < value)
+                {
+                    //  Invalid z85 encoding, represented value exceeds 0xffffffff
+                    return null;
+                }
+                value *= 85;
+                char_nbr++;
+                var index = cha - 32;
+                if (index >= Decoder.Length)
+                {
+                    //  Invalid z85 encoding, character outside range
+                    return null;
+                }
+                UInt32 summand = Decoder[index];
+                if (summand == 0xFF || summand > (UInt32.MaxValue - value))
+                {
+                    //  Invalid z85 encoding, invalid character or represented value exceeds 0xffffffff
+                    return null;
+                }
+                value += summand;
+                if (char_nbr % 5 == 0)
+                {
+                    //  Output value in base 256
+                    UInt32 divisor = 256 * 256 * 256;
+                    while (divisor != 0)
+                    {
+                        dest_.Add((byte)(value / divisor % 256));
+                        divisor /= 256;
+                    }
+                    value = 0;
+                }
+            }
+            if (char_nbr % 5 != 0)
+            {
+                return null;
+            }
+            return dest_.ToArray();
+
+        }
+
         /// <summary>
         /// Create a Certificate with a random secret key and a derived public key for the curve encryption
         /// </summary>
@@ -36,6 +147,24 @@ public NetMQCertificate(byte[] secretKey, byte[] publicKey)
             PublicKey = publicKey;
         }
 
+        /// <summary>
+        /// Create a certificate from secret key and public key
+        /// </summary>
+        /// <param name="secretKey">Secret key</param>
+        /// <param name="publicKey">Public key</param>
+        /// <exception cref="ArgumentException">If secretKey or publicKey are not 41-chars long</exception>
+        public NetMQCertificate(string secretKey, string publicKey)
+        {
+            if (secretKey.Length != 41)
+                throw new ArgumentException("secretKey must be 41 char long");
+
+            if (publicKey.Length != 41)
+                throw new ArgumentException("publicKey must be 41 char long");
+
+            SecretKey = Z85Decode(secretKey);
+            PublicKey = Z85Decode(publicKey);
+        }
+
         private NetMQCertificate(byte[] key, bool isSecret)
         {
             if (key.Length != 32)
@@ -49,7 +178,22 @@ private NetMQCertificate(byte[] key, bool isSecret)
             else
                 PublicKey = key;
         }
-
+
+        private NetMQCertificate(string keystr, bool isSecret)
+        {
+            if (keystr.Length != 41)
+                throw new ArgumentException("key must be 41 bytes length");
+
+            var key = Z85Decode(keystr);
+            if (isSecret)
+            {
+                SecretKey = key;
+                PublicKey = Curve25519.ScalarMultiplicationBase(key);
+            }
+            else
+                PublicKey = key;
+        }
+
         /// <summary>
         /// Create a certificate from secret key, public key is derived from the secret key
         /// </summary>
@@ -60,7 +204,18 @@ public NetMQCertificate FromSecretKey(byte[] secretKey)
         {
             return new NetMQCertificate(secretKey, true);
         }
-
+
+        /// <summary>
+        /// Create a certificate from secret key, public key is derived from the secret key
+        /// </summary>
+        /// <param name="secretKey">Secret Key</param>
+        /// <exception cref="ArgumentException">If secret key is not 41-chars long</exception>
+        /// <returns>The newly created certificate</returns>
+        public NetMQCertificate FromSecretKey(string secretKey)
+        {
+            return new NetMQCertificate(secretKey, true);
+        }
+
         /// <summary>
         /// Create a public key only certificate.
         /// </summary>
@@ -72,11 +227,29 @@ public static NetMQCertificate FromPublicKey(byte[] publicKey)
             return new NetMQCertificate(publicKey, false);
         }
 
+        /// <summary>
+        /// Create a public key only certificate.
+        /// </summary>
+        /// <param name="publicKey">Public key</param>
+        /// <exception cref="ArgumentException">If public key is not 41-chars long</exception>
+        /// <returns>The newly created certificate</returns>
+        public static NetMQCertificate FromPublicKey(string publicKey)
+        {
+            return new NetMQCertificate(publicKey, false);
+        }
+
         /// <summary>
         /// Curve Secret key
         /// </summary>
         public byte[]? SecretKey { get; private set; }
 
+
+        /// <summary>
+        /// Curve Public key 
+        /// </summary>
+        public string SecretKeyX85 => SecretKey != null ? Z85Encode(SecretKey) : null;
+
+
         /// <summary>
         /// Returns true if the certificate also includes a secret key
         /// </summary>
@@ -86,5 +259,13 @@ public static NetMQCertificate FromPublicKey(byte[] publicKey)
         /// Curve Public key 
         /// </summary>
         public byte[] PublicKey { get; private set; }
+
+        /// <summary>
+        /// Curve Public key 
+        /// </summary>
+        public string PublicKeyX85 
+        {
+            get => Z85Encode(PublicKey);
+        }
     }
 }