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Go code used to play around FPE / FF1 asking this question https://crypto.stackexchange.com/q/75926/1949
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package main | |
import ( | |
"encoding/hex" | |
"fmt" | |
"strings" | |
"github.com/capitalone/fpe/ff1" | |
//"alphabets" | |
) | |
// I'll be damned: https://stackoverflow.com/a/27516559/591064 | |
func min(a, b int) int { | |
if a < b { | |
return a | |
} | |
return b | |
} | |
func generateCharactersOfBase(length int) string { | |
chars := make([]rune, length) | |
i := 0 | |
soFar := 0 | |
//Start with digits | |
for ; i < min(10, length); i++ { | |
chars[i] = rune(int('0') + i) | |
} | |
soFar = i | |
//Then with uppercase letters | |
for ; i < min(26+soFar, length); i++ { | |
chars[i] = rune(int('a') + i - soFar) | |
} | |
soFar = i | |
//Now with lowercase letters | |
for ; i < min(26+soFar, length); i++ { | |
chars[i] = rune(int('A') + i - soFar) | |
} | |
return string(chars) | |
} | |
type Alphabet struct { | |
characterSet string | |
baseXDigits string | |
} | |
func (alphabet *Alphabet) Length() int { | |
return len(alphabet.characterSet) | |
} | |
func NewAlphabet(characterSet string) *Alphabet { | |
a := new(Alphabet) | |
a.characterSet = characterSet | |
a.baseXDigits = generateCharactersOfBase(len(characterSet)) | |
return a | |
} | |
func (alphabet *Alphabet) Convert(text string) string { | |
/* Equivalent Python | |
>>> import string | |
>>> base36 = list(string.digits+string.ascii_uppercase[:26-10]) | |
>>> ''.join([base36[string.ascii_uppercase.index(c)] for c in 'ABCHELLO']) | |
'01274BBE' | |
//*/ | |
chars := make([]rune, len(text)) | |
for i := 0; i < len(chars); i++ { | |
pos := strings.Index(alphabet.characterSet, string(text[i])) | |
chars[i] = rune(alphabet.baseXDigits[pos]) | |
} | |
return string(chars) | |
} | |
func (alphabet *Alphabet) Revert(text string) string { | |
/* Equivalent Python | |
>>> import string | |
>>> base36 = list(string.digits+string.ascii_uppercase[:26-10]) | |
>>> ''.join([base36[string.ascii_uppercase.index(c)] for c in 'ABCHELLO']) | |
'01274BBE' | |
//*/ | |
chars := make([]rune, len(text)) | |
for i := 0; i < len(chars); i++ { | |
pos := strings.Index(alphabet.baseXDigits, string(text[i])) | |
chars[i] = rune(alphabet.characterSet[pos]) | |
} | |
return string(chars) | |
} | |
func encryptFF1(key []byte, tweak []byte, plaintext string, alphabet *Alphabet ) string { | |
basedPlaintext := alphabet.Convert(plaintext) | |
// Create a new FF1 cipher "object" | |
// 10 is the radix/base, and 8 is the tweak length. | |
FF1, err := ff1.NewCipher(alphabet.Length(), len(tweak), key, tweak) | |
if err != nil { | |
panic(err) | |
} | |
// Call the encryption function on an example SSN | |
ciphertext, err := FF1.Encrypt(basedPlaintext) | |
if err != nil { | |
panic(err) | |
} | |
//Move the result to the original alphabet | |
return alphabet.Revert(ciphertext) | |
} | |
func decryptFF1(key []byte, tweak []byte, ciphertext string, alphabet *Alphabet ) string { | |
basedCiphertext := alphabet.Convert(ciphertext) | |
// Create a new FF1 cipher "object" | |
// 10 is the radix/base, and 8 is the tweak length. | |
FF1, err := ff1.NewCipher(alphabet.Length(), len(tweak), key, tweak) | |
if err != nil { | |
panic(err) | |
} | |
// Call the encryption function on an example SSN | |
plaintext, err := FF1.Encrypt(basedCiphertext) | |
if err != nil { | |
panic(err) | |
} | |
//Move the result to the original alphabet | |
return alphabet.Revert(plaintext) | |
} | |
// panic(err) is just used for example purposes. | |
func main() { | |
// Key and tweak should be byte arrays. Put your key and tweak here. | |
// To make it easier for demo purposes, decode from a hex string here. | |
key, err := hex.DecodeString("EF4359D8D580AA4F7F036D6F04FC6A94") | |
if err != nil { | |
panic(err) | |
} | |
tweak, err := hex.DecodeString("D8E7920AFA330A73") | |
tweak = nil | |
if err != nil { | |
panic(err) | |
} | |
a := NewAlphabet("ABCDEFGHIJKLMNOPQRSTUVWXYZ") | |
ciphertext := encryptFF1(key, tweak, "HELLO", a) | |
plaintext := decryptFF1(key, tweak, ciphertext, a) | |
fmt.Println("Ciphertext:", ciphertext) | |
fmt.Println("Plaintext:", plaintext) | |
} |
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