Add aes cryptography library

Signed-off-by: Asai Neko <sugar@sne.moe>

internal/cryptography/aes.go

@@ -0,0 +1,208 @@
+package cryptography
+
+import (
+	"bytes"
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/base64"
+	"errors"
+	"io"
+)
+
+func randomBytes(n int) ([]byte, error) {
+	b := make([]byte, n)
+	_, err := io.ReadFull(rand.Reader, b)
+	return b, err
+}
+
+func normalizeKey(key []byte) ([]byte, error) {
+	switch len(key) {
+	case 16, 24, 32:
+		return key, nil
+	default:
+		return nil, errors.New("AES key length must be 16, 24, or 32 bytes")
+	}
+}
+
+func AESGCMEncrypt(plaintext, key []byte) (string, error) {
+	key, err := normalizeKey(key)
+	if err != nil {
+		return "", err
+	}
+
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+
+	nonce, err := randomBytes(gcm.NonceSize())
+	if err != nil {
+		return "", err
+	}
+
+	ciphertext := gcm.Seal(nil, nonce, plaintext, nil)
+	out := append(nonce, ciphertext...)
+
+	return base64.RawURLEncoding.EncodeToString(out), nil
+}
+
+func AESGCMDecrypt(encoded string, key []byte) ([]byte, error) {
+	key, err := normalizeKey(key)
+	if err != nil {
+		return nil, err
+	}
+
+	data, err := base64.RawURLEncoding.DecodeString(encoded)
+	if err != nil {
+		return nil, err
+	}
+
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(data) < gcm.NonceSize() {
+		return nil, errors.New("ciphertext too short")
+	}
+
+	nonce := data[:gcm.NonceSize()]
+	ciphertext := data[gcm.NonceSize():]
+
+	return gcm.Open(nil, nonce, ciphertext, nil)
+}
+
+func pkcs7Pad(data []byte, blockSize int) []byte {
+	padding := blockSize - len(data)%blockSize
+	padtext := bytes.Repeat([]byte{byte(padding)}, padding)
+	return append(data, padtext...)
+}
+
+func pkcs7Unpad(data []byte) ([]byte, error) {
+	length := len(data)
+	if length == 0 {
+		return nil, errors.New("invalid padding")
+	}
+	padding := int(data[length-1])
+	if padding == 0 || padding > length {
+		return nil, errors.New("invalid padding")
+	}
+	return data[:length-padding], nil
+}
+
+func AESCBCEncrypt(plaintext, key []byte) (string, error) {
+	key, err := normalizeKey(key)
+	if err != nil {
+		return "", err
+	}
+
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+
+	plaintext = pkcs7Pad(plaintext, block.BlockSize())
+
+	iv, err := randomBytes(block.BlockSize())
+	if err != nil {
+		return "", err
+	}
+
+	mode := cipher.NewCBCEncrypter(block, iv)
+	mode.CryptBlocks(plaintext, plaintext)
+
+	out := append(iv, plaintext...)
+	return base64.RawURLEncoding.EncodeToString(out), nil
+}
+
+func AESCBCDecrypt(encoded string, key []byte) ([]byte, error) {
+	key, err := normalizeKey(key)
+	if err != nil {
+		return nil, err
+	}
+
+	data, err := base64.RawURLEncoding.DecodeString(encoded)
+	if err != nil {
+		return nil, err
+	}
+
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(data) < block.BlockSize() {
+		return nil, errors.New("ciphertext too short")
+	}
+
+	iv := data[:block.BlockSize()]
+	data = data[block.BlockSize():]
+
+	mode := cipher.NewCBCDecrypter(block, iv)
+	mode.CryptBlocks(data, data)
+
+	return pkcs7Unpad(data)
+}
+
+func AESCFBEncrypt(plaintext, key []byte) (string, error) {
+	key, err := normalizeKey(key)
+	if err != nil {
+		return "", err
+	}
+
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+
+	iv, err := randomBytes(block.BlockSize())
+	if err != nil {
+		return "", err
+	}
+
+	stream := cipher.NewCFBEncrypter(block, iv)
+	stream.XORKeyStream(plaintext, plaintext)
+
+	out := append(iv, plaintext...)
+	return base64.RawURLEncoding.EncodeToString(out), nil
+}
+
+func AESCFBDecrypt(encoded string, key []byte) ([]byte, error) {
+	key, err := normalizeKey(key)
+	if err != nil {
+		return nil, err
+	}
+
+	data, err := base64.RawURLEncoding.DecodeString(encoded)
+	if err != nil {
+		return nil, err
+	}
+
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(data) < block.BlockSize() {
+		return nil, errors.New("ciphertext too short")
+	}
+
+	iv := data[:block.BlockSize()]
+	data = data[block.BlockSize():]
+
+	stream := cipher.NewCFBDecrypter(block, iv)
+	stream.XORKeyStream(data, data)
+
+	return data, nil
+}