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// Copyright 2010 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 tls

import (
        "crypto/aes"
        "crypto/cipher"
        "crypto/des"
        "crypto/hmac"
        "crypto/rc4"
        "crypto/sha1"
        "crypto/x509"
        "hash"
)

// a keyAgreement implements the client and server side of a TLS key agreement
// protocol by generating and processing key exchange messages.
type keyAgreement interface {
        // On the server side, the first two methods are called in order.

        // In the case that the key agreement protocol doesn't use a
        // ServerKeyExchange message, generateServerKeyExchange can return nil,
        // nil.
        generateServerKeyExchange(*Config, *clientHelloMsg, *serverHelloMsg) (*serverKeyExchangeMsg, error)
        processClientKeyExchange(*Config, *clientKeyExchangeMsg, uint16) ([]byte, error)

        // On the client side, the next two methods are called in order.

        // This method may not be called if the server doesn't send a
        // ServerKeyExchange message.
        processServerKeyExchange(*Config, *clientHelloMsg, *serverHelloMsg, *x509.Certificate, *serverKeyExchangeMsg) error
        generateClientKeyExchange(*Config, *clientHelloMsg, *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error)
}

// A cipherSuite is a specific combination of key agreement, cipher and MAC
// function. All cipher suites currently assume RSA key agreement.
type cipherSuite struct {
        id uint16
        // the lengths, in bytes, of the key material needed for each component.
        keyLen int
        macLen int
        ivLen  int
        ka     func() keyAgreement
        // If elliptic is set, a server will only consider this ciphersuite if
        // the ClientHello indicated that the client supports an elliptic curve
        // and point format that we can handle.
        elliptic bool
        cipher   func(key, iv []byte, isRead bool) interface{}
        mac      func(version uint16, macKey []byte) macFunction
}

var cipherSuites = []*cipherSuite{
        {TLS_RSA_WITH_RC4_128_SHA, 16, 20, 0, rsaKA, false, cipherRC4, macSHA1},
        {TLS_RSA_WITH_3DES_EDE_CBC_SHA, 24, 20, 8, rsaKA, false, cipher3DES, macSHA1},
        {TLS_RSA_WITH_AES_128_CBC_SHA, 16, 20, 16, rsaKA, false, cipherAES, macSHA1},
        {TLS_ECDHE_RSA_WITH_RC4_128_SHA, 16, 20, 0, ecdheRSAKA, true, cipherRC4, macSHA1},
        {TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA, 24, 20, 8, ecdheRSAKA, true, cipher3DES, macSHA1},
        {TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA, 16, 20, 16, ecdheRSAKA, true, cipherAES, macSHA1},
}

func cipherRC4(key, iv []byte, isRead bool) interface{} {
        cipher, _ := rc4.NewCipher(key)
        return cipher
}

func cipher3DES(key, iv []byte, isRead bool) interface{} {
        block, _ := des.NewTripleDESCipher(key)
        if isRead {
                return cipher.NewCBCDecrypter(block, iv)
        }
        return cipher.NewCBCEncrypter(block, iv)
}

func cipherAES(key, iv []byte, isRead bool) interface{} {
        block, _ := aes.NewCipher(key)
        if isRead {
                return cipher.NewCBCDecrypter(block, iv)
        }
        return cipher.NewCBCEncrypter(block, iv)
}

// macSHA1 returns a macFunction for the given protocol version.
func macSHA1(version uint16, key []byte) macFunction {
        if version == versionSSL30 {
                mac := ssl30MAC{
                        h:   sha1.New(),
                        key: make([]byte, len(key)),
                }
                copy(mac.key, key)
                return mac
        }
        return tls10MAC{hmac.New(sha1.New, key)}
}

type macFunction interface {
        Size() int
        MAC(digestBuf, seq, data []byte) []byte
}

// ssl30MAC implements the SSLv3 MAC function, as defined in
// www.mozilla.org/projects/security/pki/nss/ssl/draft302.txt section 5.2.3.1
type ssl30MAC struct {
        h   hash.Hash
        key []byte
}

func (s ssl30MAC) Size() int {
        return s.h.Size()
}

var ssl30Pad1 = [48]byte{0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36, 0x36}

var ssl30Pad2 = [48]byte{0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c}

func (s ssl30MAC) MAC(digestBuf, seq, record []byte) []byte {
        padLength := 48
        if s.h.Size() == 20 {
                padLength = 40
        }

        s.h.Reset()
        s.h.Write(s.key)
        s.h.Write(ssl30Pad1[:padLength])
        s.h.Write(seq)
        s.h.Write(record[:1])
        s.h.Write(record[3:5])
        s.h.Write(record[recordHeaderLen:])
        digestBuf = s.h.Sum(digestBuf[:0])

        s.h.Reset()
        s.h.Write(s.key)
        s.h.Write(ssl30Pad2[:padLength])
        s.h.Write(digestBuf)
        return s.h.Sum(digestBuf[:0])
}

// tls10MAC implements the TLS 1.0 MAC function. RFC 2246, section 6.2.3.
type tls10MAC struct {
        h hash.Hash
}

func (s tls10MAC) Size() int {
        return s.h.Size()
}

func (s tls10MAC) MAC(digestBuf, seq, record []byte) []byte {
        s.h.Reset()
        s.h.Write(seq)
        s.h.Write(record)
        return s.h.Sum(digestBuf[:0])
}

func rsaKA() keyAgreement {
        return rsaKeyAgreement{}
}

func ecdheRSAKA() keyAgreement {
        return new(ecdheRSAKeyAgreement)
}

// mutualCipherSuite returns a cipherSuite given a list of supported
// ciphersuites and the id requested by the peer.
func mutualCipherSuite(have []uint16, want uint16) *cipherSuite {
        for _, id := range have {
                if id == want {
                        for _, suite := range cipherSuites {
                                if suite.id == want {
                                        return suite
                                }
                        }
                        return nil
                }
        }
        return nil
}

// A list of the possible cipher suite ids. Taken from
// http://www.iana.org/assignments/tls-parameters/tls-parameters.xml
const (
        TLS_RSA_WITH_RC4_128_SHA            uint16 = 0x0005
        TLS_RSA_WITH_3DES_EDE_CBC_SHA       uint16 = 0x000a
        TLS_RSA_WITH_AES_128_CBC_SHA        uint16 = 0x002f
        TLS_ECDHE_RSA_WITH_RC4_128_SHA      uint16 = 0xc011
        TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA uint16 = 0xc012
        TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA  uint16 = 0xc013
)