Source: block.go in package golang.org/x/crypto/blowfish


package blowfish

getNextWord returns the next big-endian uint32 value from the byte slice at the given position in a circular manner, updating the position.

func getNextWord(b []byte, pos *int) uint32 {
	var w uint32
	j := *pos
	for i := 0; i < 4; i++ {
		w = w<<8 | uint32(b[j])
		j++
		if j >= len(b) {
			j = 0
		}
	}
	*pos = j
	return w
}

ExpandKey performs a key expansion on the given *Cipher. Specifically, it performs the Blowfish algorithm's key schedule which sets up the *Cipher's pi and substitution tables for calls to Encrypt. This is used, primarily, by the bcrypt package to reuse the Blowfish key schedule during its set up. It's unlikely that you need to use this directly.

func ExpandKey(key []byte, c *Cipher) {
	j := 0

Using inlined getNextWord for performance.

		var d uint32
		for k := 0; k < 4; k++ {
			d = d<<8 | uint32(key[j])
			j++
			if j >= len(key) {
				j = 0
			}
		}
		c.p[i] ^= d
	}

	var l, r uint32
	for i := 0; i < 18; i += 2 {
		l, r = encryptBlock(l, r, c)
		c.p[i], c.p[i+1] = l, r
	}

	for i := 0; i < 256; i += 2 {
		l, r = encryptBlock(l, r, c)
		c.s0[i], c.s0[i+1] = l, r
	}
	for i := 0; i < 256; i += 2 {
		l, r = encryptBlock(l, r, c)
		c.s1[i], c.s1[i+1] = l, r
	}
	for i := 0; i < 256; i += 2 {
		l, r = encryptBlock(l, r, c)
		c.s2[i], c.s2[i+1] = l, r
	}
	for i := 0; i < 256; i += 2 {
		l, r = encryptBlock(l, r, c)
		c.s3[i], c.s3[i+1] = l, r
	}
}

This is similar to ExpandKey, but folds the salt during the key schedule. While ExpandKey is essentially expandKeyWithSalt with an all-zero salt passed in, reusing ExpandKey turns out to be a place of inefficiency and specializing it here is useful.

func expandKeyWithSalt(key []byte, salt []byte, c *Cipher) {
	j := 0
	for i := 0; i < 18; i++ {
		c.p[i] ^= getNextWord(key, &j)
	}

	j = 0
	var l, r uint32
	for i := 0; i < 18; i += 2 {
		l ^= getNextWord(salt, &j)
		r ^= getNextWord(salt, &j)
		l, r = encryptBlock(l, r, c)
		c.p[i], c.p[i+1] = l, r
	}

	for i := 0; i < 256; i += 2 {
		l ^= getNextWord(salt, &j)
		r ^= getNextWord(salt, &j)
		l, r = encryptBlock(l, r, c)
		c.s0[i], c.s0[i+1] = l, r
	}

	for i := 0; i < 256; i += 2 {
		l ^= getNextWord(salt, &j)
		r ^= getNextWord(salt, &j)
		l, r = encryptBlock(l, r, c)
		c.s1[i], c.s1[i+1] = l, r
	}

	for i := 0; i < 256; i += 2 {
		l ^= getNextWord(salt, &j)
		r ^= getNextWord(salt, &j)
		l, r = encryptBlock(l, r, c)
		c.s2[i], c.s2[i+1] = l, r
	}

	for i := 0; i < 256; i += 2 {
		l ^= getNextWord(salt, &j)
		r ^= getNextWord(salt, &j)
		l, r = encryptBlock(l, r, c)
		c.s3[i], c.s3[i+1] = l, r
	}
}

func encryptBlock(l, r uint32, c *Cipher) (uint32, uint32) {
	xl, xr := l, r
	xl ^= c.p[0]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[1]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[2]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[3]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[4]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[5]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[6]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[7]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[8]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[9]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[10]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[11]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[12]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[13]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[14]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[15]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[16]
	xr ^= c.p[17]
	return xr, xl
}

func decryptBlock(l, r uint32, c *Cipher) (uint32, uint32) {
	xl, xr := l, r
	xl ^= c.p[17]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[16]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[15]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[14]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[13]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[12]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[11]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[10]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[9]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[8]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[7]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[6]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[5]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[4]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[3]
	xr ^= ((c.s0[byte(xl>>24)] + c.s1[byte(xl>>16)]) ^ c.s2[byte(xl>>8)]) + c.s3[byte(xl)] ^ c.p[2]
	xl ^= ((c.s0[byte(xr>>24)] + c.s1[byte(xr>>16)]) ^ c.s2[byte(xr>>8)]) + c.s3[byte(xr)] ^ c.p[1]
	xr ^= c.p[0]
	return xr, xl