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108 lines
3 KiB
Go
108 lines
3 KiB
Go
// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package tea implements the TEA algorithm, as defined in Needham and
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// Wheeler's 1994 technical report, “TEA, a Tiny Encryption Algorithm”. See
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// http://www.cix.co.uk/~klockstone/tea.pdf for details.
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package tea
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import (
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"crypto/cipher"
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"encoding/binary"
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"errors"
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)
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const (
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// BlockSize is the size of a TEA block, in bytes.
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BlockSize = 8
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// KeySize is the size of a TEA key, in bytes.
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KeySize = 16
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// delta is the TEA key schedule constant.
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delta = 0x9e3779b9
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// numRounds is the standard number of rounds in TEA.
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numRounds = 64
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)
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// tea is an instance of the TEA cipher with a particular key.
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type tea struct {
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key [16]byte
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rounds int
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}
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// NewCipher returns an instance of the TEA cipher with the standard number of
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// rounds. The key argument must be 16 bytes long.
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func NewCipher(key []byte) (cipher.Block, error) {
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return NewCipherWithRounds(key, numRounds)
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}
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// NewCipherWithRounds returns an instance of the TEA cipher with a given
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// number of rounds, which must be even. The key argument must be 16 bytes
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// long.
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func NewCipherWithRounds(key []byte, rounds int) (cipher.Block, error) {
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if len(key) != 16 {
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return nil, errors.New("tea: incorrect key size")
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}
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if rounds&1 != 0 {
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return nil, errors.New("tea: odd number of rounds specified")
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}
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c := &tea{
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rounds: rounds,
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}
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copy(c.key[:], key)
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return c, nil
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}
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// BlockSize returns the TEA block size, which is eight bytes. It is necessary
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// to satisfy the Block interface in the package "crypto/cipher".
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func (*tea) BlockSize() int {
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return BlockSize
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}
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// Encrypt encrypts the 8 byte buffer src using the key in t and stores the
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// result in dst. Note that for amounts of data larger than a block, it is not
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// safe to just call Encrypt on successive blocks; instead, use an encryption
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// mode like CBC (see crypto/cipher/cbc.go).
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func (t *tea) Encrypt(dst, src []byte) {
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e := binary.BigEndian
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v0, v1 := e.Uint32(src), e.Uint32(src[4:])
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k0, k1, k2, k3 := e.Uint32(t.key[0:]), e.Uint32(t.key[4:]), e.Uint32(t.key[8:]), e.Uint32(t.key[12:])
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sum := uint32(0)
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delta := uint32(delta)
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for i := 0; i < t.rounds/2; i++ {
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sum += delta
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v0 += ((v1 << 4) + k0) ^ (v1 + sum) ^ ((v1 >> 5) + k1)
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v1 += ((v0 << 4) + k2) ^ (v0 + sum) ^ ((v0 >> 5) + k3)
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}
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e.PutUint32(dst, v0)
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e.PutUint32(dst[4:], v1)
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}
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// Decrypt decrypts the 8 byte buffer src using the key in t and stores the
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// result in dst.
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func (t *tea) Decrypt(dst, src []byte) {
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e := binary.BigEndian
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v0, v1 := e.Uint32(src), e.Uint32(src[4:])
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k0, k1, k2, k3 := e.Uint32(t.key[0:]), e.Uint32(t.key[4:]), e.Uint32(t.key[8:]), e.Uint32(t.key[12:])
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delta := uint32(delta)
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sum := delta * uint32(t.rounds/2) // in general, sum = delta * n
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for i := 0; i < t.rounds/2; i++ {
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v1 -= ((v0 << 4) + k2) ^ (v0 + sum) ^ ((v0 >> 5) + k3)
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v0 -= ((v1 << 4) + k0) ^ (v1 + sum) ^ ((v1 >> 5) + k1)
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sum -= delta
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}
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e.PutUint32(dst, v0)
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e.PutUint32(dst[4:], v1)
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}
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