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// Copyright 2009 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/hmac"

        "crypto/md5"

        "crypto/sha1"

        "hash"

)

// Split a premaster secret in two as specified in RFC 4346, section 5.

func splitPreMasterSecret(secret []byte) (s1, s2 []byte) {

        s1 = secret[0 : (len(secret)+1)/2]

        s2 = secret[len(secret)/2:]

        return

}

// pHash implements the P_hash function, as defined in RFC 4346, section 5.

func pHash(result, secret, seed []byte, hash func() hash.Hash) {

        h := hmac.New(hash, secret)

        h.Write(seed)

        a := h.Sum(nil)

        j := 0

        for j < len(result) {

                h.Reset()

                h.Write(a)

                h.Write(seed)

                b := h.Sum(nil)

                todo := len(b)

                if j+todo > len(result) {

                        todo = len(result) - j

                }

                copy(result[j:j+todo], b)

                j += todo

                h.Reset()

                h.Write(a)

                a = h.Sum(nil)

        }

}

// pRF10 implements the TLS 1.0 pseudo-random function, as defined in RFC 2246, section 5.

func pRF10(result, secret, label, seed []byte) {

        hashSHA1 := sha1.New

        hashMD5 := md5.New

        labelAndSeed := make([]byte, len(label)+len(seed))

        copy(labelAndSeed, label)

        copy(labelAndSeed[len(label):], seed)

        s1, s2 := splitPreMasterSecret(secret)

        pHash(result, s1, labelAndSeed, hashMD5)

        result2 := make([]byte, len(result))

        pHash(result2, s2, labelAndSeed, hashSHA1)

        for i, b := range result2 {

                result[i] ^= b

        }

}

// pRF30 implements the SSL 3.0 pseudo-random function, as defined in

// www.mozilla.org/projects/security/pki/nss/ssl/draft302.txt section 6.

func pRF30(result, secret, label, seed []byte) {

        hashSHA1 := sha1.New()

        hashMD5 := md5.New()

        done := 0

        i := 0

        // RFC5246 section 6.3 says that the largest PRF output needed is 128

        // bytes. Since no more ciphersuites will be added to SSLv3, this will

        // remain true. Each iteration gives us 16 bytes so 10 iterations will

        // be sufficient.

        var b [11]byte

        for done < len(result) {

                for j := 0; j <= i; j++ {

                        b[j] = 'A' + byte(i)

                }

                hashSHA1.Reset()

                hashSHA1.Write(b[:i+1])

                hashSHA1.Write(secret)

                hashSHA1.Write(seed)

                digest := hashSHA1.Sum(nil)

                hashMD5.Reset()

                hashMD5.Write(secret)

                hashMD5.Write(digest)

                done += copy(result[done:], hashMD5.Sum(nil))

                i++

        }

}

const (

        tlsRandomLength      = 32 // Length of a random nonce in TLS 1.1.

        masterSecretLength   = 48 // Length of a master secret in TLS 1.1.

        finishedVerifyLength = 12 // Length of verify_data in a Finished message.

)

var masterSecretLabel = []byte("master secret")

var keyExpansionLabel = []byte("key expansion")

var clientFinishedLabel = []byte("client finished")

var serverFinishedLabel = []byte("server finished")

// keysFromPreMasterSecret generates the connection keys from the pre master

// secret, given the lengths of the MAC key, cipher key and IV, as defined in

// RFC 2246, section 6.3.

func keysFromPreMasterSecret(version uint16, preMasterSecret, clientRandom, serverRandom []byte, macLen, keyLen, ivLen int) (masterSecret, clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV []byte) {

        prf := pRF10

        if version == versionSSL30 {

                prf = pRF30

        }

        var seed [tlsRandomLength * 2]byte

        copy(seed[0:len(clientRandom)], clientRandom)

        copy(seed[len(clientRandom):], serverRandom)

        masterSecret = make([]byte, masterSecretLength)

        prf(masterSecret, preMasterSecret, masterSecretLabel, seed[0:])

        copy(seed[0:len(clientRandom)], serverRandom)

        copy(seed[len(serverRandom):], clientRandom)

        n := 2*macLen + 2*keyLen + 2*ivLen

        keyMaterial := make([]byte, n)

        prf(keyMaterial, masterSecret, keyExpansionLabel, seed[0:])

        clientMAC = keyMaterial[:macLen]

        keyMaterial = keyMaterial[macLen:]

        serverMAC = keyMaterial[:macLen]

        keyMaterial = keyMaterial[macLen:]

        clientKey = keyMaterial[:keyLen]

        keyMaterial = keyMaterial[keyLen:]

        serverKey = keyMaterial[:keyLen]

        keyMaterial = keyMaterial[keyLen:]

        clientIV = keyMaterial[:ivLen]

        keyMaterial = keyMaterial[ivLen:]

        serverIV = keyMaterial[:ivLen]

        return

}

func newFinishedHash(version uint16) finishedHash {

        return finishedHash{md5.New(), sha1.New(), md5.New(), sha1.New(), version}

}

// A finishedHash calculates the hash of a set of handshake messages suitable

// for including in a Finished message.

type finishedHash struct {

        clientMD5  hash.Hash

        clientSHA1 hash.Hash

        serverMD5  hash.Hash

        serverSHA1 hash.Hash

        version    uint16

}

func (h finishedHash) Write(msg []byte) (n int, err error) {

        h.clientMD5.Write(msg)

        h.clientSHA1.Write(msg)

        h.serverMD5.Write(msg)

        h.serverSHA1.Write(msg)

        return len(msg), nil

}

// finishedSum10 calculates the contents of the verify_data member of a TLSv1

// Finished message given the MD5 and SHA1 hashes of a set of handshake

// messages.

func finishedSum10(md5, sha1, label, masterSecret []byte) []byte {

        seed := make([]byte, len(md5)+len(sha1))

        copy(seed, md5)

        copy(seed[len(md5):], sha1)

        out := make([]byte, finishedVerifyLength)

        pRF10(out, masterSecret, label, seed)

        return out

}

// finishedSum30 calculates the contents of the verify_data member of a SSLv3

// Finished message given the MD5 and SHA1 hashes of a set of handshake

// messages.

func finishedSum30(md5, sha1 hash.Hash, masterSecret []byte, magic [4]byte) []byte {

        md5.Write(magic[:])

        md5.Write(masterSecret)

        md5.Write(ssl30Pad1[:])

        md5Digest := md5.Sum(nil)

        md5.Reset()

        md5.Write(masterSecret)

        md5.Write(ssl30Pad2[:])

        md5.Write(md5Digest)

        md5Digest = md5.Sum(nil)

        sha1.Write(magic[:])

        sha1.Write(masterSecret)

        sha1.Write(ssl30Pad1[:40])

        sha1Digest := sha1.Sum(nil)

        sha1.Reset()

        sha1.Write(masterSecret)

        sha1.Write(ssl30Pad2[:40])

        sha1.Write(sha1Digest)

        sha1Digest = sha1.Sum(nil)

        ret := make([]byte, len(md5Digest)+len(sha1Digest))

        copy(ret, md5Digest)

        copy(ret[len(md5Digest):], sha1Digest)

        return ret

}

var ssl3ClientFinishedMagic = [4]byte{0x43, 0x4c, 0x4e, 0x54}

var ssl3ServerFinishedMagic = [4]byte{0x53, 0x52, 0x56, 0x52}

// clientSum returns the contents of the verify_data member of a client's

// Finished message.

func (h finishedHash) clientSum(masterSecret []byte) []byte {

        if h.version == versionSSL30 {

                return finishedSum30(h.clientMD5, h.clientSHA1, masterSecret, ssl3ClientFinishedMagic)

        }

        md5 := h.clientMD5.Sum(nil)

        sha1 := h.clientSHA1.Sum(nil)

        return finishedSum10(md5, sha1, clientFinishedLabel, masterSecret)

}

// serverSum returns the contents of the verify_data member of a server's

// Finished message.

func (h finishedHash) serverSum(masterSecret []byte) []byte {

        if h.version == versionSSL30 {

                return finishedSum30(h.serverMD5, h.serverSHA1, masterSecret, ssl3ServerFinishedMagic)

        }

        md5 := h.serverMD5.Sum(nil)

        sha1 := h.serverSHA1.Sum(nil)

        return finishedSum10(md5, sha1, serverFinishedLabel, masterSecret)

}