/usr/share/gocode/src/golang.org/x/crypto/tea/cipher.go is in golang-golang-x-crypto-dev 1:0.0~git20170407.0.55a552f+REALLY.0.0~git20161012.0.5f31782-1.
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// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package tea implements the TEA algorithm, as defined in Needham and
// Wheeler's 1994 technical report, “TEA, a Tiny Encryption Algorithm”. See
// http://www.cix.co.uk/~klockstone/tea.pdf for details.
package tea
import (
"crypto/cipher"
"encoding/binary"
"errors"
)
const (
// BlockSize is the size of a TEA block, in bytes.
BlockSize = 8
// KeySize is the size of a TEA key, in bytes.
KeySize = 16
// delta is the TEA key schedule constant.
delta = 0x9e3779b9
// numRounds is the standard number of rounds in TEA.
numRounds = 64
)
// tea is an instance of the TEA cipher with a particular key.
type tea struct {
key [16]byte
rounds int
}
// NewCipher returns an instance of the TEA cipher with the standard number of
// rounds. The key argument must be 16 bytes long.
func NewCipher(key []byte) (cipher.Block, error) {
return NewCipherWithRounds(key, numRounds)
}
// NewCipherWithRounds returns an instance of the TEA cipher with a given
// number of rounds, which must be even. The key argument must be 16 bytes
// long.
func NewCipherWithRounds(key []byte, rounds int) (cipher.Block, error) {
if len(key) != 16 {
return nil, errors.New("tea: incorrect key size")
}
if rounds&1 != 0 {
return nil, errors.New("tea: odd number of rounds specified")
}
c := &tea{
rounds: rounds,
}
copy(c.key[:], key)
return c, nil
}
// BlockSize returns the TEA block size, which is eight bytes. It is necessary
// to satisfy the Block interface in the package "crypto/cipher".
func (*tea) BlockSize() int {
return BlockSize
}
// Encrypt encrypts the 8 byte buffer src using the key in t and stores the
// result in dst. Note that for amounts of data larger than a block, it is not
// safe to just call Encrypt on successive blocks; instead, use an encryption
// mode like CBC (see crypto/cipher/cbc.go).
func (t *tea) Encrypt(dst, src []byte) {
e := binary.BigEndian
v0, v1 := e.Uint32(src), e.Uint32(src[4:])
k0, k1, k2, k3 := e.Uint32(t.key[0:]), e.Uint32(t.key[4:]), e.Uint32(t.key[8:]), e.Uint32(t.key[12:])
sum := uint32(0)
delta := uint32(delta)
for i := 0; i < t.rounds/2; i++ {
sum += delta
v0 += ((v1 << 4) + k0) ^ (v1 + sum) ^ ((v1 >> 5) + k1)
v1 += ((v0 << 4) + k2) ^ (v0 + sum) ^ ((v0 >> 5) + k3)
}
e.PutUint32(dst, v0)
e.PutUint32(dst[4:], v1)
}
// Decrypt decrypts the 8 byte buffer src using the key in t and stores the
// result in dst.
func (t *tea) Decrypt(dst, src []byte) {
e := binary.BigEndian
v0, v1 := e.Uint32(src), e.Uint32(src[4:])
k0, k1, k2, k3 := e.Uint32(t.key[0:]), e.Uint32(t.key[4:]), e.Uint32(t.key[8:]), e.Uint32(t.key[12:])
delta := uint32(delta)
sum := delta * uint32(t.rounds/2) // in general, sum = delta * n
for i := 0; i < t.rounds/2; i++ {
v1 -= ((v0 << 4) + k2) ^ (v0 + sum) ^ ((v0 >> 5) + k3)
v0 -= ((v1 << 4) + k0) ^ (v1 + sum) ^ ((v1 >> 5) + k1)
sum -= delta
}
e.PutUint32(dst, v0)
e.PutUint32(dst[4:], v1)
}
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