1 files changed, 150 insertions, 0 deletions
diff --git a/crypto/src/util/ssh/SSHBuffer.cs b/crypto/src/util/ssh/SSHBuffer.cs
new file mode 100644
index 000000000..8d3c3f977
--- /dev/null
+++ b/crypto/src/util/ssh/SSHBuffer.cs
@@ -0,0 +1,150 @@
+using System;
+using Org.BouncyCastle.Math;
+
+namespace Org.BouncyCastle.Utilities.SSH
+{
+    public class SSHBuffer
+    {
+        private readonly byte[] buffer;
+        private int pos = 0;
+
+        public SSHBuffer(byte[] magic, byte[] buffer)
+        {
+            this.buffer = buffer;
+            for (int i = 0; i != magic.Length; i++)
+            {
+                if (magic[i] != buffer[i])
+                {
+                    throw new ArgumentException("magic-number incorrect");
+                }
+            }
+
+            pos += magic.Length;
+        }
+
+        public SSHBuffer(byte[] buffer)
+        {
+            this.buffer = buffer;
+        }
+
+        public int ReadU32()
+        {
+            if (pos > (buffer.Length - 4))
+            {
+                throw new ArgumentOutOfRangeException("4 bytes for U32 exceeds buffer.");
+            }
+
+            int i = (buffer[pos++] & 0xFF) << 24;
+            i |= (buffer[pos++] & 0xFF) << 16;
+            i |= (buffer[pos++] & 0xFF) << 8;
+            i |= (buffer[pos++] & 0xFF);
+
+            return i;
+        }
+
+        public String ReadString()
+        {
+            return Strings.FromByteArray(ReadBlock());
+        }
+
+        public byte[] ReadBlock()
+        {
+            int len = ReadU32();
+            if (len == 0)
+            {
+                return new byte[0];
+            }
+
+            if (pos > (buffer.Length - len))
+            {
+                throw new ArgumentException("not enough data for block");
+            }
+
+            int start = pos; pos += len;
+            return Arrays.CopyOfRange(buffer, start, pos);
+        }
+
+        public void SkipBlock()
+        {
+            int len = ReadU32();
+            if (pos > (buffer.Length - len))
+            {
+                throw new ArgumentException("not enough data for block");
+            }
+
+            pos += len;
+        }
+
+        public byte[] ReadPaddedBlock()
+        {
+            return ReadPaddedBlock(8);
+        }
+
+        public byte[] ReadPaddedBlock(int blockSize)
+        {
+            int len = ReadU32();
+            if (len == 0)
+            {
+                return new byte[0];
+            }
+
+            if (pos > (buffer.Length - len))
+            {
+                throw new ArgumentException("not enough data for block");
+            }
+
+            int align = len % blockSize;
+            if (0 != align)
+            {
+                throw new ArgumentException("missing padding");
+            }
+
+            int start = pos; pos += len;
+            int end = pos;
+
+            if (len > 0)
+            {
+                // TODO If encryption is supported, should be constant-time
+                int lastByte = buffer[pos - 1] & 0xFF;
+                if (0 < lastByte && lastByte < blockSize)
+                {
+                    int padCount = lastByte;
+                    end -= padCount;
+
+                    for (int i = 1, padPos = end; i <= padCount; ++i, ++padPos)
+                    {
+                        if (i != (buffer[padPos] & 0xFF))
+                        {
+                            throw new ArgumentException("incorrect padding");
+                        }
+                    }
+                }
+            }
+
+            return Arrays.CopyOfRange(buffer, start, end);
+        }
+
+        public BigInteger ReadBigNumPositive()
+        {
+            int len = ReadU32();
+            if (pos + len > buffer.Length)
+            {
+                throw new ArgumentException("not enough data for big num");
+            }
+
+            int start = pos; pos += len;
+            byte[] d = Arrays.CopyOfRange(buffer, start, pos);
+            return new BigInteger(1, d);
+        }
+
+        public byte[] GetBuffer()
+        {
+            return Arrays.Clone(buffer);
+        }
+
+        public Boolean HasRemaining()
+        {
+            return pos < buffer.Length;
+        }
+    }
+}