libsodium in PHP 7
About me
About me
Cryptography is...
... the practice and study of techniques for secure communication in the presence of third parties called adversaries
... about constructing and analyzing protocols that prevent third parties or the public from reading private messagesWikipedia
Cryptography is...
Plaintext
→
←
Encryption
Decryption
Ciphertext
42a14c854f
Symmetric Cryptography
Uses the same key for both encryption and decryption
Also known as Secret-key Cryptography
Symmetric Cryptography
public function encrypt($data) {
$iv = random_bytes(
openssl_cipher_iv_length('aes-256-ctr')
);
$ciphertext = openssl_encrypt(
$data,
'aes-256-ctr', // cipher
'@rw97`b#1,EquJ[L2P2', // key
OPENSSL_RAW_DATA, // flags
$iv // iv (nonce)
);
return base64_encode(
$iv . $ciphertext
);
}
Simple symmetric cryptography example using OpenSSL
Symmetric Cryptography
public function encrypt($data) {
$iv = random_bytes(
openssl_cipher_iv_length('aes-256-gcm')
);
$ciphertext = openssl_encrypt(
$data,
'aes-256-gcm', // cipher
'@rw97`b#1,EquJ[L2P2', // key
OPENSSL_RAW_DATA, // flags
$iv, // iv (nonce)
$tag, // tag
null, // aad
16 // tag length
);
return base64_encode(
$iv . $tag . $ciphertext
);
}
Simple symmetric cryptography example using OpenSSL
Symmetric Cryptography
public function decrypt($data) {
$data = base64_decode($data);
$ivSize = openssl_cipher_iv_length('aes-256-ctr');
$iv = substr($data, 0, $ivSize);
$data = substr($data, $ivSize);
return openssl_decrypt(
$data,
'aes-256-ctr', // cipher
'@rw97`b#1,EquJ[L2P2', // key
OPENSSL_RAW_DATA, // flags
$iv // iv (nonce)
);
}
Simple symmetric cryptography example using OpenSSL
Asymmetric Cryptography
Public key
Can be distributed to others
Private key
Must remain with the owner
Also known as Public-key Cryptography
Asymmetric Cryptography
If you want others to communicate with you...
Public key
Used by them to write texts to you
↓
Encryption
Private key
Used by you to read those texts
↓
Decryption
Asymmetric Cryptography
If you want to communicate with others...
Public key
Used by them to verify the texts were written by you
↓
Decryption
Private key
Used by you to write texts
↓
Encryption
Asymmetric Cryptography
public function encrypt(
string $data,
string $publicKeyPath
): string {
$public = openssl_pkey_get_public(
"file://{$publicKeyPath}"
);
if (! openssl_public_encrypt($data, $crypted, $public)) {
throw new \RuntimeException("Can't encrypt data");
}
return $crypted;
}
Simple asymmetric cryptography using OpenSSL
Asymmetric Cryptography
public function decrypt(
string $data,
string $privateKeyPath,
string $passphrase = null
): string {
$key = openssl_pkey_get_private(
"file://{$privateKeyPath}",
$passphrase
);
if (! openssl_private_decrypt($data, $decrypted, $key)) {
throw new \RuntimeException("Can't decrypt data");
}
return $decrypted;
}
Simple asymmetric cryptography using OpenSSL
Asymmetric Cryptography
But I'm sure that instead of omitting that
$padding parameter in the previous codes,
we always use OPENSSL_PKCS1_OAEP_PADDING, right?
Asymmetric Cryptography
After all, it's pretty obvious that the default
OPENSSL_PKCS1_PADDING value uses PKCS#1 v1.5,
which is vulnerable to Padding attacks
Asymmetric Cryptography
And it's common knowledge that the RSA algorithm with a 2048 bit key can't handle data blocks larger than 214 bytes
RIGHT?
Hashing
A hash function is any function that can be used to map data of arbitrary size to fixed-size valuesWikipedia
Hashing
But I already know how to use that
if (hash('sha512', $_POST['password']) !== $storedPassword) {
throw new InvalidCredentialsException();
}
Hashing
But do you know about Timing Attacks?
is a side-channel attack in which the attacker attempts to compromise a cryptosystem by analyzing the time taken to execute cryptographic algorithmsWikipedia
Hashing
And what about Rainbow Tables?
is a precomputed table for caching the output of cryptographic hash functionsWikipedia
libsodium
- Modern library available since PHP 7.2
- Fork of NaCl
- Official website: libsodium.org
- Full documentation: pecl libsodium
- GitHub: libsodium-php
Symmetric Cryptography
// APP_SECRET_KEY should be
// SODIUM_CRYPTO_BOX_SECRETKEYBYTES bytes long
// Generates a random nonce
$nonce = random_bytes(SODIUM_CRYPTO_SECRETBOX_NONCEBYTES);
$ciphertext = sodium_crypto_secretbox(
$plaintext,
$nonce,
APP_SECRET_KEY
);
// Prefixing nonce so we can retrieve it when decrypting
$ciphertext = sodium_bin2hex($nonce . $ciphertext);
Symmetric Cryptography
$ciphertext = sodium_hex2bin($ciphertext);
// Retrieving nonce
$nonce = substr(
$ciphertext,
0,
SODIUM_CRYPTO_SECRETBOX_NONCEBYTES
);
$ciphertext = substr(
$ciphertext,
SODIUM_CRYPTO_SECRETBOX_NONCEBYTES
);
// Decrypting
$plaintext = sodium_crypto_secretbox_open(
$ciphertext,
$nonce,
APP_SECRET_KEY
);
Authentication
// APP_AUTH_KEY should be
// SODIUM_CRYPTO_AUTH_KEYBYTES bytes long
// Authenticates the specified ciphertext
$auth = sodium_bin2hex(
sodium_crypto_auth($ciphertext, APP_AUTH_KEY)
);
Authentication
$auth = sodium_hex2bin($auth);
// Validates authentication data
if (! sodium_crypto_auth_verify(
$auth,
$ciphertext,
APP_AUTH_KEY
)) {
throw new RuntimeException('Authentication failed');
}
Asymmetric Cryptography
// User #1 (Alice)
$aliceKeyPair = sodium_crypto_box_keypair();
$alicePublic = sodium_crypto_box_publickey($aliceKeyPair);
$aliceSecret = sodium_crypto_box_secretkey($aliceKeyPair);
// User #2 (Bob)
$bobKeyPair = sodium_crypto_box_keypair();
$bobPublic = sodium_crypto_box_publickey($bobKeyPair);
$bobSecret = sodium_crypto_box_secretkey($bobKeyPair);
Asymmetric Cryptography
// User #1 (Alice)
$nonce = random_bytes(SODIUM_CRYPTO_BOX_NONCEBYTES);
$key = sodium_crypto_box_keypair_from_secretkey_and_publickey(
$aliceSecret,
$bobPublic
);
$encrypted = sodium_crypto_box($message, $nonce, $key);
$ciphertext = $nonce . $encrypted;
Asymmetric Cryptography
// User #2 (Bob)
$nonce = substr($ciphertext, 0, SODIUM_CRYPTO_BOX_NONCEBYTES);
$ciphertext = substr($ciphertext, SODIUM_CRYPTO_BOX_NONCEBYTES);
$key = sodium_crypto_box_keypair_from_secretkey_and_publickey(
$bobSecret,
$alicePublic
);
echo sodium_crypto_box_open($encrypted, $nonce, $key);
Storing passwords
sodium_crypto_pwhash_str(
$password,
SODIUM_CRYPTO_PWHASH_OPSLIMIT_INTERACTIVE,
SODIUM_CRYPTO_PWHASH_MEMLIMIT_INTERACTIVE
);
// $argon2id$v=19$m=65536,t=2,p=1$20H8uU9EFq7GO2NFPrfDyg$Om/qimxzk9/7mub1s7b ...
Validating passwords
sodium_crypto_pwhash_str_verify(
$storedPassword,
$inputPassword
);
More examples!
Recap
- Cryptography is not easy
- DO NOT use your own algorithms , unless you are a competition-winner cryptologist
- You CAN use OpenSSL and others libraries (like phpseclib), as long as you know what you're doing (and what they're doing too)
- To be safe, always use modern and up-to-date solutions