aes.NewCipher returns a valid block, but I get an error when calling block.BlockSize()

Question

I'm trying to get AES encryption and decryption working in my go API, I create a new block using aes.NewCipher(mykey) and the block seems to be valid, but then when I call cipher.NewCBCDecrypter(block, iv) the function causes a "invalid memory address or nil pointer dereference" error at line 26 in cbc.go when it tries to call b.BlockSize().

So I tried calling block.BlockSize() from my own code and I also get an exception, but when I check the block var it's not nil.

func Decrypt(data []byte) (result []byte, err error) {
    logger := logrus.New()

    logger.Infof("Starting decryption for string: %s\n", string(data[:]))

    var block cipher.Block

    if block, err := aes.NewCipher([]byte(app.Config.AESKey)); (err != nil) || (block == nil) {
        logger.Infof("Failed to create block\n")
        return nil, err
    }

    if len(data) < aes.BlockSize {
        logger.Infof("Input too short\n")
        return nil, nil
    }

    cbc := cipher.NewCBCDecrypter(block, []byte(app.Config.AESIV))
    cbc.CryptBlocks(data, data)

    return data, nil
}

I would expect the function to work properly since aes.NewCipher doesn't return an error.

Answer 1

Remove this line

var block cipher.Block

As you are initializing block in the next line.

Essentially, you are creating 2 block variables.