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package crypto
import (
"bytes"
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"io"
)
// EncryptAESCBC - use a 128, 192, or 256 bit key to encrypt the given content
// using AES-CBC. The output will not be encoded. Usually the output would be
// base64-encoded for display. Empty content will not be encrypted.
//
// This function is compatible with Helm's decryptAES function, when the output
// is base64-encoded, and when the key is 256 bits long.
func EncryptAESCBC(key []byte, in []byte) ([]byte, error) {
if len(in) == 0 {
return in, nil
}
block, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
// Pad the content to be a multiple of the block size, with the pad length
// as the content. Note that the padding will be a full block when the
// content is already a multiple of the block size.
// This algorithm is described in the TLS spec:
// https://datatracker.ietf.org/doc/html/rfc5246#section-6.2.3.2
bs := block.BlockSize()
pl := bs - len(in)%bs
// pad with pl, repeated pl times
in = append(in, bytes.Repeat([]byte{byte(pl)}, pl)...)
out := make([]byte, bs+len(in))
// Generate a random IV. Must be the same length as the block size, and is
// stored at the beginning of the output slice unencrypted, so that it can
// be used for decryption.
iv := out[:bs]
if _, err := io.ReadFull(rand.Reader, iv); err != nil {
return nil, err
}
// encrypt the content into the rest of the output slice
mode := cipher.NewCBCEncrypter(block, iv)
mode.CryptBlocks(out[bs:], in)
return out, nil
}
// DecryptAESCBC - use a 128, 192, or 256 bit key to decrypt the given content
// using AES-CBC. The output will not be encoded. Empty content will not be
// decrypted.
//
// This function is compatible with Helm's encryptAES function, when the input
// is base64-decoded, and when the key is 256 bits long.
func DecryptAESCBC(key []byte, in []byte) ([]byte, error) {
if len(in) == 0 {
return nil, nil
}
block, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
// the first block is the IV, unencrypted
iv := in[:aes.BlockSize]
// the rest of the content is encrypted
in = in[aes.BlockSize:]
out := make([]byte, len(in))
mode := cipher.NewCBCDecrypter(block, iv)
mode.CryptBlocks(out, in)
// content must always be padded with at least one byte, and the padding
// byte must be the padding length
pl := int(out[len(out)-1])
out = out[:len(out)-pl]
return out, nil
}
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