MD5crypt.go

package md5crypt

import (
	"crypto/md5"
	"fmt"
	"strings"
	"testing"
)

func TestMD5crypt(t *testing.T) {
	result := MD5crypt([]byte("1234"), []byte("GVYkFcwv"), []byte("$1$"))
	fmt.Println(result)
	if result != "$1$GVYkFcwv$wzUAmJjs/zNImk6jT2UjN." {
		t.Errorf("Invalid result: %s", result)
	}
}

const itoa64 = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"

var (
	arr = [][]int{
		[]int{0, 6, 12},
		[]int{1, 7, 13},
		[]int{2, 8, 14},
		[]int{3, 9, 15},
		[]int{4, 10, 5},
	}
)

func MD5crypt(rawPass, salt, magic []byte) string {
	hash := md5.New()
	hash.Write(rawPass)
	hash.Write(magic)
	hash.Write(salt)

	st := md5.New()
	st.Write(rawPass)
	st.Write(salt)
	st.Write(rawPass)
	stretch := st.Sum(nil)
	for i := 0; i < len(rawPass); i++ {
		hash.Write([]byte{stretch[i%16]})
	}

	i := len(rawPass)

	for i > 0 {
		if i&1 > 0 {
			hash.Write([]byte{0})
		} else {
			hash.Write([]byte{rawPass[0]})
		}
		i >>= 1
	}

	saltedMD5 := hash.Sum(nil)
	for i = 0; i < 1000; i++ {
		hash.Reset()
		if i&1 > 0 {
			hash.Write(rawPass)
		} else {
			hash.Write(saltedMD5)
		}

		if i%3 > 0 {
			hash.Write(salt)
		}
		if i%7 > 0 {
			hash.Write(rawPass)
		}
		if i&1 > 0 {
			hash.Write(saltedMD5)
		} else {
			hash.Write(rawPass)
		}

		saltedMD5 = hash.Sum(nil)
	}

	builder := strings.Builder{}
	builder.WriteString(string(magic))
	builder.WriteString(string(salt))
	builder.WriteRune('$')
	for _, subArr := range arr {
		v := int(saltedMD5[subArr[0]])<<16 |
			int(saltedMD5[subArr[1]])<<8 |
			int(saltedMD5[subArr[2]])
		for i := 0; i < 4; i++ {
			builder.WriteRune(rune(itoa64[v&0x3f]))
			v >>= 6
		}
	}

	v := int(saltedMD5[11])
	for i := 0; i < 2; i++ {
		builder.WriteRune(rune(itoa64[v&0x3f]))
		v >>= 6
	}

	return builder.String()
}