84 lines
1.9 KiB
Go
84 lines
1.9 KiB
Go
package aescbc
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import (
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"bytes"
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"crypto/aes"
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"crypto/cipher"
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"errors"
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"fmt"
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)
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const KeySize = 32
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func EncryptPkcs7(key []byte, iv []byte, plaintext []byte) ([]byte, error) {
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plaintext = pkcs7Padding(plaintext)
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return EncryptNoPadding(key, iv, plaintext)
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}
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func EncryptNoPadding(key []byte, iv []byte, plaintext []byte) ([]byte, error) {
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if len(key) != KeySize {
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return nil, fmt.Errorf("invalid key size, expected %v, got %v", KeySize, len(key))
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}
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block, err := aes.NewCipher(key)
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if err != nil {
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return nil, err
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}
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ciphertext := make([]byte, len(plaintext))
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mode := cipher.NewCBCEncrypter(block, iv)
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mode.CryptBlocks(ciphertext, plaintext)
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return ciphertext, nil
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}
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func DecryptPkcs7(key []byte, iv []byte, cypertext []byte) ([]byte, error) {
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paddedPlaintext, err := DecryptNoPadding(key, iv, cypertext)
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if err != nil {
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return nil, err
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}
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return pkcs7UnPadding(paddedPlaintext)
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}
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func DecryptNoPadding(key []byte, iv []byte, cypertext []byte) ([]byte, error) {
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if len(key) != KeySize {
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return nil, fmt.Errorf("invalid key size, expected %v, got %v", KeySize, len(key))
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}
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block, err := aes.NewCipher(key)
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if err != nil {
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return nil, err
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}
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plaintext := make([]byte, len(cypertext))
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mode := cipher.NewCBCDecrypter(block, iv)
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mode.CryptBlocks(plaintext, cypertext)
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return plaintext, nil
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}
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func pkcs7Padding(src []byte) []byte {
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padding := aes.BlockSize - len(src)%aes.BlockSize
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padtext := bytes.Repeat([]byte{byte(padding)}, padding)
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return append(src, padtext...)
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}
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func pkcs7UnPadding(src []byte) ([]byte, error) {
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length := len(src)
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unpadding := int(src[length-1])
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if unpadding > aes.BlockSize || unpadding == 0 {
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return nil, errors.New("invalid pkcs7 padding (unpadding > aes.BlockSize || unpadding == 0)")
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}
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pad := src[len(src)-unpadding:]
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for i := 0; i < unpadding; i++ {
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if pad[i] != byte(unpadding) {
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return nil, errors.New("invalid pkcs7 padding (pad[i] != unpadding)")
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}
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}
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return src[:(length - unpadding)], nil
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}
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