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package pkcs7
import (
"bytes"
"crypto"
"crypto/aes"
"crypto/cipher"
"crypto/des"
"crypto/rand"
"crypto/rsa"
"crypto/x509"
"encoding/asn1"
"errors"
"fmt"
)
// ErrUnsupportedAlgorithm tells you when our quick dev assumptions have failed
var ErrUnsupportedAlgorithm = errors.New("pkcs7: cannot decrypt data: only RSA, DES, DES-EDE3, AES-256-CBC and AES-128-GCM supported")
// ErrNotEncryptedContent is returned when attempting to Decrypt data that is not encrypted data
var ErrNotEncryptedContent = errors.New("pkcs7: content data is a decryptable data type")
// Decrypt decrypts encrypted content info for recipient cert and private key
func (p7 *PKCS7) Decrypt(cert *x509.Certificate, pkey crypto.PrivateKey) ([]byte, error) {
data, ok := p7.raw.(envelopedData)
if !ok {
return nil, ErrNotEncryptedContent
}
recipient := selectRecipientForCertificate(data.RecipientInfos, cert)
if recipient.EncryptedKey == nil {
return nil, errors.New("pkcs7: no enveloped recipient for provided certificate")
}
switch pkey := pkey.(type) {
case *rsa.PrivateKey:
var contentKey []byte
contentKey, err := rsa.DecryptPKCS1v15(rand.Reader, pkey, recipient.EncryptedKey)
if err != nil {
return nil, err
}
return data.EncryptedContentInfo.decrypt(contentKey)
}
return nil, ErrUnsupportedAlgorithm
}
// DecryptUsingPSK decrypts encrypted data using caller provided
// pre-shared secret
func (p7 *PKCS7) DecryptUsingPSK(key []byte) ([]byte, error) {
data, ok := p7.raw.(encryptedData)
if !ok {
return nil, ErrNotEncryptedContent
}
return data.EncryptedContentInfo.decrypt(key)
}
func (eci encryptedContentInfo) decrypt(key []byte) ([]byte, error) {
alg := eci.ContentEncryptionAlgorithm.Algorithm
if !alg.Equal(OIDEncryptionAlgorithmDESCBC) &&
!alg.Equal(OIDEncryptionAlgorithmDESEDE3CBC) &&
!alg.Equal(OIDEncryptionAlgorithmAES256CBC) &&
!alg.Equal(OIDEncryptionAlgorithmAES128CBC) &&
!alg.Equal(OIDEncryptionAlgorithmAES128GCM) &&
!alg.Equal(OIDEncryptionAlgorithmAES256GCM) {
fmt.Printf("Unsupported Content Encryption Algorithm: %s\n", alg)
return nil, ErrUnsupportedAlgorithm
}
// EncryptedContent can either be constructed of multple OCTET STRINGs
// or _be_ a tagged OCTET STRING
var cyphertext []byte
if eci.EncryptedContent.IsCompound {
// Complex case to concat all of the children OCTET STRINGs
var buf bytes.Buffer
cypherbytes := eci.EncryptedContent.Bytes
for {
var part []byte
cypherbytes, _ = asn1.Unmarshal(cypherbytes, &part)
buf.Write(part)
if cypherbytes == nil {
break
}
}
cyphertext = buf.Bytes()
} else {
// Simple case, the bytes _are_ the cyphertext
cyphertext = eci.EncryptedContent.Bytes
}
var block cipher.Block
var err error
switch {
case alg.Equal(OIDEncryptionAlgorithmDESCBC):
block, err = des.NewCipher(key)
case alg.Equal(OIDEncryptionAlgorithmDESEDE3CBC):
block, err = des.NewTripleDESCipher(key)
case alg.Equal(OIDEncryptionAlgorithmAES256CBC), alg.Equal(OIDEncryptionAlgorithmAES256GCM):
fallthrough
case alg.Equal(OIDEncryptionAlgorithmAES128GCM), alg.Equal(OIDEncryptionAlgorithmAES128CBC):
block, err = aes.NewCipher(key)
}
if err != nil {
return nil, err
}
if alg.Equal(OIDEncryptionAlgorithmAES128GCM) || alg.Equal(OIDEncryptionAlgorithmAES256GCM) {
params := aesGCMParameters{}
paramBytes := eci.ContentEncryptionAlgorithm.Parameters.Bytes
_, err := asn1.Unmarshal(paramBytes, ¶ms)
if err != nil {
return nil, err
}
gcm, err := cipher.NewGCM(block)
if err != nil {
return nil, err
}
if len(params.Nonce) != gcm.NonceSize() {
return nil, errors.New("pkcs7: encryption algorithm parameters are incorrect")
}
if params.ICVLen != gcm.Overhead() {
return nil, errors.New("pkcs7: encryption algorithm parameters are incorrect")
}
plaintext, err := gcm.Open(nil, params.Nonce, cyphertext, nil)
if err != nil {
return nil, err
}
return plaintext, nil
}
iv := eci.ContentEncryptionAlgorithm.Parameters.Bytes
if len(iv) != block.BlockSize() {
return nil, errors.New("pkcs7: encryption algorithm parameters are malformed")
}
mode := cipher.NewCBCDecrypter(block, iv)
plaintext := make([]byte, len(cyphertext))
mode.CryptBlocks(plaintext, cyphertext)
if plaintext, err = unpad(plaintext, mode.BlockSize()); err != nil {
return nil, err
}
return plaintext, nil
}
func unpad(data []byte, blocklen int) ([]byte, error) {
if blocklen < 1 {
return nil, fmt.Errorf("invalid blocklen %d", blocklen)
}
if len(data)%blocklen != 0 || len(data) == 0 {
return nil, fmt.Errorf("invalid data len %d", len(data))
}
// the last byte is the length of padding
padlen := int(data[len(data)-1])
// check padding integrity, all bytes should be the same
pad := data[len(data)-padlen:]
for _, padbyte := range pad {
if padbyte != byte(padlen) {
return nil, errors.New("invalid padding")
}
}
return data[:len(data)-padlen], nil
}
func selectRecipientForCertificate(recipients []recipientInfo, cert *x509.Certificate) recipientInfo {
for _, recp := range recipients {
if isCertMatchForIssuerAndSerial(cert, recp.IssuerAndSerialNumber) {
return recp
}
}
return recipientInfo{}
}
|
