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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)
}