cipher32.go

package rc5

import (
    "crypto/cipher"
    "encoding/binary"
    "math/bits"
)

const (
    // BlockSize the RC5/32 block size in bytes.
    BlockSize32 = 8
    P32         = 0xB7E15163
    Q32         = 0x9E3779B9
)

type rc5Cipher32 struct {
    rounds uint
    rk     []uint32
}

func newCipher32(key []byte, rounds uint) (cipher.Block, error) {
    c := &rc5Cipher32{}
    c.rounds = rounds
    c.rk = make([]uint32, (rounds+1)<<1)
    c.expandKey(key)
    return c, nil
}

func (c *rc5Cipher32) BlockSize() int {
    return BlockSize32
}

func (c *rc5Cipher32) Encrypt(dst, src []byte) {
    if len(src) < BlockSize32 {
        panic("cryptobin/rc5-32: input not full block")
    }

    if len(dst) < BlockSize32 {
        panic("cryptobin/rc5-32: output not full block")
    }

    if inexactOverlap(dst[:BlockSize32], src[:BlockSize32]) {
        panic("cryptobin/rc5-32: invalid buffer overlap")
    }

    A := binary.LittleEndian.Uint32(src[:4]) + c.rk[0]
    B := binary.LittleEndian.Uint32(src[4:BlockSize32]) + c.rk[1]

    for r := 1; r <= int(c.rounds); r++ {
        A = bits.RotateLeft32(A^B, int(B)) + c.rk[r<<1]
        B = bits.RotateLeft32(B^A, int(A)) + c.rk[r<<1+1]
    }

    binary.LittleEndian.PutUint32(dst[:4], A)
    binary.LittleEndian.PutUint32(dst[4:8], B)
}

func (c *rc5Cipher32) Decrypt(dst, src []byte) {
    if len(src) < BlockSize32 {
        panic("cryptobin/rc5-32: input not full block")
    }

    if len(dst) < BlockSize32 {
        panic("cryptobin/rc5-32: output not full block")
    }

    if inexactOverlap(dst[:BlockSize32], src[:BlockSize32]) {
        panic("cryptobin/rc5-32: invalid buffer overlap")
    }

    A := binary.LittleEndian.Uint32(src[:4])
    B := binary.LittleEndian.Uint32(src[4:8])

    for r := c.rounds; r >= 1; r-- {
        B = A ^ bits.RotateLeft32(B-c.rk[r<<1+1], -int(A))
        A = B ^ bits.RotateLeft32(A-c.rk[r<<1], -int(B))
    }

    binary.LittleEndian.PutUint32(dst[:4], A-c.rk[0])
    binary.LittleEndian.PutUint32(dst[4:8], B-c.rk[1])
}

func (c *rc5Cipher32) expandKey(key []byte) {
    rk := c.rk

    roundKeys := len(rk)

    // L is initially a c-length list of 0-valued w-length words
    L := make([]uint32, len(key)/4)
    lenL := len(L)
    for i := 0; i < lenL; i++ {
        L[i] = binary.LittleEndian.Uint32(key[:4])
        key = key[4:]
    }

    // Initialize key-independent pseudorandom S array
    // S is initially a t=2(r+1) length list of undefined w-length words
    rk[0] = P32
    for i := 1; i < roundKeys; i++ {
        rk[i] = rk[i-1] + Q32
    }

    // The main key scheduling loop
    var A uint32
    var B uint32
    var i, j int
    for k := 0; k < 3*roundKeys; k++ {
        rk[i] = bits.RotateLeft32(rk[i]+(A+B), 3)
        A = rk[i]
        L[j] = bits.RotateLeft32(L[j]+(A+B), int(A+B))
        B = L[j]
        i = (i + 1) % roundKeys
        j = (j + 1) % lenL
    }
}