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102 lines
2.7 KiB
Go
102 lines
2.7 KiB
Go
/*
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CBC describes a block cipher mode. In cryptography, a block cipher mode of operation is an algorithm that uses a
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block cipher to provide an information service such as confidentiality or authenticity. A block cipher by itself
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is only suitable for the secure cryptographic transformation (encryption or decryption) of one fixed-length group of
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bits called a block. A mode of operation describes how to repeatedly apply a cipher's single-block operation to
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securely transform amounts of data larger than a block.
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This package simplifies the usage of AES-256-CBC.
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*/
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package cipher
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/*
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Some code is provided by the GitHub user locked (github.com/locked):
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https://gist.github.com/locked/b066aa1ddeb2b28e855e
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Thanks!
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*/
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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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"crypto/rand"
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"fmt"
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"io"
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)
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/*
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Decrypt is a function that decrypts a given cipher text with a provided key and initialization vector(iv).
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*/
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func DecryptCbc(iv, key, ciphertext []byte) ([]byte, error) {
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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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if len(ciphertext) < aes.BlockSize {
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return nil, fmt.Errorf("ciphertext is shorter then block size: %d / %d", len(ciphertext), aes.BlockSize)
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}
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if iv == nil {
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iv = ciphertext[:aes.BlockSize]
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ciphertext = ciphertext[aes.BlockSize:]
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}
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cbc := cipher.NewCBCDecrypter(block, iv)
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cbc.CryptBlocks(ciphertext, ciphertext)
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return unpad(ciphertext)
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}
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/*
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Encrypt is a function that encrypts plaintext with a given key and an optional initialization vector(iv).
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*/
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func EncryptCbc(iv, key, plaintext []byte) ([]byte, error) {
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plaintext = pad(plaintext, aes.BlockSize)
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if len(plaintext)%aes.BlockSize != 0 {
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return nil, fmt.Errorf("plaintext is not a multiple of the block size: %d / %d", len(plaintext), aes.BlockSize)
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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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var ciphertext []byte
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if iv == nil {
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ciphertext = make([]byte, aes.BlockSize+len(plaintext))
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iv := ciphertext[:aes.BlockSize]
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if _, err := io.ReadFull(rand.Reader, iv); err != nil {
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return nil, err
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}
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cbc := cipher.NewCBCEncrypter(block, iv)
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cbc.CryptBlocks(ciphertext[aes.BlockSize:], plaintext)
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} else {
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ciphertext = make([]byte, len(plaintext))
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cbc := cipher.NewCBCEncrypter(block, iv)
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cbc.CryptBlocks(ciphertext, plaintext)
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}
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return ciphertext, nil
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}
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func pad(ciphertext []byte, blockSize int) []byte {
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padding := blockSize - len(ciphertext)%blockSize
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padtext := bytes.Repeat([]byte{byte(padding)}, padding)
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return append(ciphertext, padtext...)
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}
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func unpad(src []byte) ([]byte, error) {
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length := len(src)
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padLen := int(src[length-1])
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if padLen > length {
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return nil, fmt.Errorf("padding is greater then the length: %d / %d", padLen, length)
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}
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return src[:(length - padLen)], nil
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}
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