iblfile_legacyenc.go

// From https://github.com/InfinityBotList/iblfile/blob/7d02b1ba186e0d6211330ae3d5442521345f90c1/consts.go
package iblfile_legacyenc

import (
	"bytes"
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"crypto/sha512"
	"crypto/x509"
	"encoding/pem"
	"fmt"
)

// The number of keys to encrypt the data with
//
// Note that changing keycount does not need a change in protocol version
const KeyCount = 16

type PemEncryptionData struct {
	// Public key to encrypt data with
	PEM []byte `json:"p"`

	// Encrypted OEAP keys
	Keys [][]byte `json:"k"`

	// Encryption nonce
	Nonce string `json:"n"`

	// Whether or not symmetric encryption is being used
	//
	// If this option is set, then a `privKey` section MUST be present (e.g. using an AutoEncrypted file)
	Symmetric bool `json:"s"`
}

func DecryptData(encData *bytes.Buffer, enc *PemEncryptionData, privkey []byte) (*bytes.Buffer, error) {
	var decrPass = []byte(enc.Nonce)
	for _, key := range enc.Keys {
		hash := sha512.New()
		random := rand.Reader

		pem, _ := pem.Decode(privkey)

		if pem == nil {
			return nil, fmt.Errorf("failed to decode private key file")
		}

		privInterface, parseErr := x509.ParsePKCS8PrivateKey(pem.Bytes)

		if parseErr != nil {
			return nil, fmt.Errorf("failed to parse private key: %s", parseErr)
		}

		priv := privInterface.(*rsa.PrivateKey)
		msg, err := rsa.DecryptOAEP(hash, random, priv, key, nil)

		if err != nil {
			return nil, fmt.Errorf("failed to decrypt data: %s", err)
		}

		decrPass = append(decrPass, msg...)
	}

	// Decrypt backupBuf with encryptedKey using aes-512-gcm
	keyHash := sha256.New()
	keyHash.Write(decrPass)
	c, err := aes.NewCipher(keyHash.Sum(nil))

	if err != nil {
		return nil, fmt.Errorf("failed to create cipher: %s", err)
	}

	gcm, err := cipher.NewGCM(c)

	if err != nil {
		return nil, fmt.Errorf("failed to create gcm: %s", err)
	}

	nonceSize := gcm.NonceSize()
	// Extract nonce from encrypted data which is a bytes buffer
	aesNonce := encData.Next(nonceSize)

	if len(aesNonce) != nonceSize {
		return nil, fmt.Errorf("failed to extract nonce from encrypted data: %d != %d", len(aesNonce), nonceSize)
	}

	encData = bytes.NewBuffer(encData.Bytes())

	// Decrypt data
	decData, err := gcm.Open(nil, aesNonce, encData.Bytes(), nil)

	if err != nil {
		return nil, fmt.Errorf("failed to decrypt data: %s", err)
	}

	return bytes.NewBuffer(decData), nil
}