Add dependencies/vendor (whatsapp)

vendor/go.mau.fi/libsignal/cipher/Cbc.go

@@ -0,0 +1,101 @@
+/*
+CBC describes a block cipher mode. In cryptography, a block cipher mode of operation is an algorithm that uses a
+block cipher to provide an information service such as confidentiality or authenticity. A block cipher by itself
+is only suitable for the secure cryptographic transformation (encryption or decryption) of one fixed-length group of
+bits called a block. A mode of operation describes how to repeatedly apply a cipher's single-block operation to
+securely transform amounts of data larger than a block.
+
+This package simplifies the usage of AES-256-CBC.
+*/
+package cipher
+
+/*
+Some code is provided by the GitHub user locked (github.com/locked):
+https://gist.github.com/locked/b066aa1ddeb2b28e855e
+Thanks!
+*/
+import (
+	"bytes"
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"fmt"
+	"io"
+)
+
+/*
+Decrypt is a function that decrypts a given cipher text with a provided key and initialization vector(iv).
+*/
+func DecryptCbc(iv, key, ciphertext []byte) ([]byte, error) {
+	block, err := aes.NewCipher(key)
+
+	if err != nil {
+		return nil, err
+	}
+
+	if len(ciphertext) < aes.BlockSize {
+		return nil, fmt.Errorf("ciphertext is shorter then block size: %d / %d", len(ciphertext), aes.BlockSize)
+	}
+
+	if iv == nil {
+		iv = ciphertext[:aes.BlockSize]
+		ciphertext = ciphertext[aes.BlockSize:]
+	}
+
+	cbc := cipher.NewCBCDecrypter(block, iv)
+	cbc.CryptBlocks(ciphertext, ciphertext)
+
+	return unpad(ciphertext)
+}
+
+/*
+Encrypt is a function that encrypts plaintext with a given key and an optional initialization vector(iv).
+*/
+func EncryptCbc(iv, key, plaintext []byte) ([]byte, error) {
+	plaintext = pad(plaintext, aes.BlockSize)
+
+	if len(plaintext)%aes.BlockSize != 0 {
+		return nil, fmt.Errorf("plaintext is not a multiple of the block size: %d / %d", len(plaintext), aes.BlockSize)
+	}
+
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+
+	var ciphertext []byte
+	if iv == nil {
+		ciphertext = make([]byte, aes.BlockSize+len(plaintext))
+		iv := ciphertext[:aes.BlockSize]
+		if _, err := io.ReadFull(rand.Reader, iv); err != nil {
+			return nil, err
+		}
+
+		cbc := cipher.NewCBCEncrypter(block, iv)
+		cbc.CryptBlocks(ciphertext[aes.BlockSize:], plaintext)
+	} else {
+		ciphertext = make([]byte, len(plaintext))
+
+		cbc := cipher.NewCBCEncrypter(block, iv)
+		cbc.CryptBlocks(ciphertext, plaintext)
+	}
+
+	return ciphertext, nil
+}
+
+func pad(ciphertext []byte, blockSize int) []byte {
+	padding := blockSize - len(ciphertext)%blockSize
+	padtext := bytes.Repeat([]byte{byte(padding)}, padding)
+	return append(ciphertext, padtext...)
+}
+
+func unpad(src []byte) ([]byte, error) {
+	length := len(src)
+	padLen := int(src[length-1])
+
+	if padLen > length {
+		return nil, fmt.Errorf("padding is greater then the length: %d / %d", padLen, length)
+	}
+
+	return src[:(length - padLen)], nil
+}