Go AES CBC Examples

gistfile1.txt

package main

import (
    "crypto/aes"
    "crypto/cipher"
    "fmt"
    "crypto/rand"
    "io"
    "encoding/base64"
    "encoding/hex"
)

func Unpad(src []byte) []byte {
    length := len(src)
    unpadding := int(src[length-1])
    return src[:(length - unpadding)]
}

func main() {
    var ciphertext, plaintext []byte
    var err error

    // The key length can be 32, 24, 16  bytes (OR in bits: 128, 192 or 256)
    key := []byte("longer means more possible keys ")
    plaintext = []byte("longer MEANS more POSSIBLE keys ")

    if ciphertext, err = encryptCBC(key, plaintext); err != nil {
        panic(err)
    }
    cleartext := base64.StdEncoding.EncodeToString(ciphertext[aes.BlockSize:])
    fmt.Printf("CBC: %s\n", cleartext)

    if plaintext, err = decryptCBC(key, ciphertext); err != nil {
        panic(err)
    }
    fmt.Printf("Clear from CBC: %s\n", plaintext)

    // echo 'dev' | openssl enc -aes-256-cbc -nosalt -K 6c6f6e676572206d65616e73206d6f726520706f737369626c65206b65797320 -iv acfa7a047800b2f221f2c4f7d626eafb | base64 + add IV padding first
    //enc, _ := base64.StdEncoding.DecodeString("rPp6BHgAsvIh8sT31ibq+xX5Kc/0uBTewwk+lCd5v0M=")
    enc, _ := base64.StdEncoding.DecodeString("Tz3w9bV7G/DOa2R8yCTU4LwmT/ahQ9sWRNEMtBXIUuQ=")
    test_key := []byte("HELP ME !!")
    // Pad key
    padded := make([]byte, 32)
    copy(padded, []byte(test_key))
    if plaintext, err = decryptCBC(padded, enc); err != nil {
        panic(err)
    }
    // We need to unpad plaintext
    fmt.Printf("padded key: %s plain: %s\n", padded, Unpad(plaintext))
}


// CBC
func encryptCBC(key, plaintext []byte) (ciphertext []byte, err error) {
    if len(plaintext)%aes.BlockSize != 0 {
        panic("plaintext is not a multiple of the block size")
    }

    block, err := aes.NewCipher(key)
    if err != nil {
        panic(err)
    }

    ciphertext = make([]byte, aes.BlockSize+len(plaintext))
    iv := ciphertext[:aes.BlockSize]
    if _, err := io.ReadFull(rand.Reader, iv); err != nil {
        panic(err)
    }
    //iv, _ := hex.DecodeString("acfa7a047800b2f221f2c4f7d626eafb")
    //copy(ciphertext[:aes.BlockSize], iv)

    fmt.Printf("CBC Key: %s\n", hex.EncodeToString(key))
    fmt.Printf("CBC IV: %s\n", hex.EncodeToString(iv))

    cbc := cipher.NewCBCEncrypter(block, iv)
    cbc.CryptBlocks(ciphertext[aes.BlockSize:], plaintext)

    return
}
func decryptCBC(key, ciphertext []byte) (plaintext []byte, err error) {
    var block cipher.Block

    if block, err = aes.NewCipher(key); err != nil {
        return
    }

    if len(ciphertext) < aes.BlockSize {
        fmt.Printf("ciphertext too short")
        return
    }

    iv := ciphertext[:aes.BlockSize]
    ciphertext = ciphertext[aes.BlockSize:]

    cbc := cipher.NewCBCDecrypter(block, iv)
    cbc.CryptBlocks(ciphertext, ciphertext)

    plaintext = ciphertext

    return
}