private.go

// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package ssh

// Copy only of used functions from message.go, common.go

import (
	"encoding/binary"
	"math/big"
)

const (
	kexAlgoDH1SHA1  = "diffie-hellman-group1-sha1"
	kexAlgoDH14SHA1 = "diffie-hellman-group14-sha1"
	kexAlgoECDH256  = "ecdh-sha2-nistp256"
	kexAlgoECDH384  = "ecdh-sha2-nistp384"
	kexAlgoECDH521  = "ecdh-sha2-nistp521"
)

var bigOne = big.NewInt(1)

func stringLength(n int) int {
	return 4 + n
}

// MarshalPublicKey serializes a supported key or certificate for use
// by the SSH wire protocol. It can be used for comparison with the
// pubkey argument of ServerConfig's PublicKeyCallback as well as for
// generating an authorized_keys or host_keys file.
func MarshalPublicKey(key PublicKey) []byte {
	// See also RFC 4253 6.6.
	algoname := key.PublicKeyAlgo()
	blob := key.Marshal()

	length := stringLength(len(algoname))
	length += len(blob)
	ret := make([]byte, length)
	r := marshalString(ret, []byte(algoname))
	copy(r, blob)
	return ret
}

func parseInt(in []byte) (out *big.Int, rest []byte, ok bool) {
	contents, rest, ok := parseString(in)
	if !ok {
		return
	}
	out = new(big.Int)

	if len(contents) > 0 && contents[0]&0x80 == 0x80 {
		// This is a negative number
		notBytes := make([]byte, len(contents))
		for i := range notBytes {
			notBytes[i] = ^contents[i]
		}
		out.SetBytes(notBytes)
		out.Add(out, bigOne)
		out.Neg(out)
	} else {
		// Positive number
		out.SetBytes(contents)
	}
	ok = true
	return
}

func parseUint32(in []byte) (uint32, []byte, bool) {
	if len(in) < 4 {
		return 0, nil, false
	}
	return binary.BigEndian.Uint32(in), in[4:], true
}

func parseUint64(in []byte) (uint64, []byte, bool) {
	if len(in) < 8 {
		return 0, nil, false
	}
	return binary.BigEndian.Uint64(in), in[8:], true
}

func parseString(in []byte) (out, rest []byte, ok bool) {
	if len(in) < 4 {
		return
	}
	length := binary.BigEndian.Uint32(in)
	if uint32(len(in)) < 4+length {
		return
	}
	out = in[4 : 4+length]
	rest = in[4+length:]
	ok = true
	return
}

func intLength(n *big.Int) int {
	length := 4 /* length bytes */
	if n.Sign() < 0 {
		nMinus1 := new(big.Int).Neg(n)
		nMinus1.Sub(nMinus1, bigOne)
		bitLen := nMinus1.BitLen()
		if bitLen%8 == 0 {
			// The number will need 0xff padding
			length++
		}
		length += (bitLen + 7) / 8
	} else if n.Sign() == 0 {
		// A zero is the zero length string
	} else {
		bitLen := n.BitLen()
		if bitLen%8 == 0 {
			// The number will need 0x00 padding
			length++
		}
		length += (bitLen + 7) / 8
	}

	return length
}

func marshalUint32(to []byte, n uint32) []byte {
	binary.BigEndian.PutUint32(to, n)
	return to[4:]
}

func marshalUint64(to []byte, n uint64) []byte {
	binary.BigEndian.PutUint64(to, n)
	return to[8:]
}

func marshalInt(to []byte, n *big.Int) []byte {
	lengthBytes := to
	to = to[4:]
	length := 0

	if n.Sign() < 0 {
		// A negative number has to be converted to two's-complement
		// form. So we'll subtract 1 and invert. If the
		// most-significant-bit isn't set then we'll need to pad the
		// beginning with 0xff in order to keep the number negative.
		nMinus1 := new(big.Int).Neg(n)
		nMinus1.Sub(nMinus1, bigOne)
		bytes := nMinus1.Bytes()
		for i := range bytes {
			bytes[i] ^= 0xff
		}
		if len(bytes) == 0 || bytes[0]&0x80 == 0 {
			to[0] = 0xff
			to = to[1:]
			length++
		}
		nBytes := copy(to, bytes)
		to = to[nBytes:]
		length += nBytes
	} else if n.Sign() == 0 {
		// A zero is the zero length string
	} else {
		bytes := n.Bytes()
		if len(bytes) > 0 && bytes[0]&0x80 != 0 {
			// We'll have to pad this with a 0x00 in order to
			// stop it looking like a negative number.
			to[0] = 0
			to = to[1:]
			length++
		}
		nBytes := copy(to, bytes)
		to = to[nBytes:]
		length += nBytes
	}

	lengthBytes[0] = byte(length >> 24)
	lengthBytes[1] = byte(length >> 16)
	lengthBytes[2] = byte(length >> 8)
	lengthBytes[3] = byte(length)
	return to
}

func marshalString(to []byte, s []byte) []byte {
	to[0] = byte(len(s) >> 24)
	to[1] = byte(len(s) >> 16)
	to[2] = byte(len(s) >> 8)
	to[3] = byte(len(s))
	to = to[4:]
	copy(to, s)
	return to[len(s):]
}