The Sodium crypto library of PHP 7.2 (PHP Day 2018)

5/14/2018 The Sodium crypto library of PHP 7.2 - phpDay 2018
https://www.zimuel.it/slides/phpday2018/sodium?print-pdf#/ 1/40
© 2018 Rogue Wave Software, Inc. All Rights Reserved.
THESODIUMCRYPTOLIBRARYTHESODIUMCRYPTOLIBRARY
OFPHP7.2OFPHP7.2
by
Senior Software Engineer
, Verona (Italy), May 12
Enrico Zimuel
Rogue Wave Software, Inc.
phpDay 2018

ABOUTMEABOUTME
Developer since 1996
Senior Software Engineer at
Inc.
Core team of ,
and
and international speaker
Research Programmer at
Co-founder of (Italy)
Rogue Wave Software
Apigility
Expressive Zend Framework
TEDx
Amsterdam University
PUG Torino

OVERVIEWOVERVIEW
NaCl/Sodium libraries
Elliptic Curve Cryptography
Sodium in PHP 7.2:
1. Encrypt with a shared-key
2. Authenticate with a shared-key
3. Sending secret messages
4. Digital signature
5. AEAD AES-GCM
6. Store passwords safely
7. Derive a key from a user's password

CRYPTOGRAPHYCRYPTOGRAPHY
Cryptography is hard. Hard to design, hard to implement,
hard to use, and hard to get right.

NACLNACL
NaCl: Networking and Cryptography library
High-speed software library for network
communication, encryption, decryption, signatures, etc
by Prof. , and
Highly-secure primitives and constructions,
implemented with extreme care to avoid
Daniel J. Bernstein others
side-channel
attacks

SIDE-CHANNELATTACKSIDE-CHANNELATTACK
Attack based on information gained from the
implementation of a computer system, rather than
weaknesses in the implemented algorithm itself

DECODERSAKEYUSINGPOWERANALYSISDECODERSAKEYUSINGPOWERANALYSIS
Source: Protecting Against Side-Channel Attacks with an Ultra-Low Power Processor

TIMINGATTACKTIMINGATTACK
An attacker measures the CPU time to perform some
procedures involving a secret (e.g. encryption key). If this
time depends on the secret, the attacker may be able to
deduce information about the secret.

EXAMPLEINPHPEXAMPLEINPHP
function compare(string $expected, string $actual): bool
{
$lenExpected = strlen($expected);
$lenActual = strlen($actual);
if ($lenExpected !== $lenActual) {
return false;
}
for($i=0; $i < $lenActual; $i++) {
if ($expected[$i] !== $actual[$i]) {
return false;
}
}
return true;
}

PREVENTTIMINGATTACK*PREVENTTIMINGATTACK*
* constant-time comparison
function compare(string $expected, string $actual): bool
{
$lenExpected = strlen($expected);
$lenActual = strlen($actual);
$len = min($lenExpected, $lenActual);
$result = 0;
for ($i = 0; $i < $len; $i++) {
$result |= ord($expected[$i]) ^ ord($actual[$i]);
}
$result |= $lenExpected ^ $lenActual;
return ($result === 0);
}

BESTTIMINGATTACKBESTTIMINGATTACK
In 2006 Adi Shamir, Eran Tromer, and Dag Arne Osvik
used a timing attack to discover, in 65 milliseconds, the
secret key used in widely deployed software for hard-
disk encryption.
Source: Cache Attacks and Countermeasures: the Case of AES

SODIUMCRYPTOLIBRARYSODIUMCRYPTOLIBRARY

SODIUMSODIUM
Sodium (libsodium) is a fork of NaCl
A portable, cross-compilable, installable, packageable,
API-compatible version of NaCl
Same implementations of crypto primitives as NaCl
Shared library and a standard set of headers (portable
implementation)
O cial web site: libsodium.org

FEATURESFEATURES
Authenticated public-key and authenticated shared-
key encryption
Public-key and shared-key signatures
Hashing
Keyed hashes for short messages
Secure pseudo-random numbers generation

ALGORITHMSINSODIUMALGORITHMSINSODIUM
Di e–Hellman key-exchange function
, stream ciphers
message-authentication code
public-key signature system
, password hashing
authenticated encryption algorithm
Curve25519
Salsa20 ChaCha20
Poly1305
Ed25519
Argon2 Scrypt
AES-GCM

ELLIPTICCURVESELLIPTICCURVES

ELLIPTICCURVESELLIPTICCURVES
= + ax + by
2
x
3

ADD2POINTSADD2POINTS
A + B = C, A + C = D, A + D = E

SCALARMULTIPLICATIONSCALARMULTIPLICATION
Given and nd such that is hard
P + P = 2P
P Q k Q = kP

SODIUMINPHPSODIUMINPHP
Available (as standard library) from PHP 7.2
PECL extension ( ) for PHP 7.0/7.1
85 functions with pre x sodium_
e.g. sodium_crypto_box_keypair()
libsodium

EXAMPLE1:EXAMPLE1:
ENCRYPTWITHASHARED-KEYENCRYPTWITHASHARED-KEY

SYMMETRICENCRYPTIONSYMMETRICENCRYPTION
Note: the encryption is always authenticated, you need to store also nonce + ciphertext
Algorithms: to encrypt and for MAC
$msg = 'This is a super secret message!';
// Generating an encryption key and a nonce
$key = random_bytes(SODIUM_CRYPTO_SECRETBOX_KEYBYTES); // 256 bit
$nonce = random_bytes(SODIUM_CRYPTO_SECRETBOX_NONCEBYTES); // 24 bytes
// Encrypt
$ciphertext = sodium_crypto_secretbox($msg, $nonce, $key);
// Decrypt
$plaintext = sodium_crypto_secretbox_open($ciphertext, $nonce, $key);
echo $plaintext === $msg ? 'Success' : 'Error';
XSalsa20 Poly1305

EXAMPLE2:EXAMPLE2:
AUTHENTICATEWITHASHARED-KEYAUTHENTICATEWITHASHARED-KEY

SYMMETRICAUTHENTICATIONSYMMETRICAUTHENTICATION
Note: the message is not encrypted
Algorithm:
$msg = 'This is the message to authenticate!';
$key = random_bytes(SODIUM_CRYPTO_SECRETBOX_KEYBYTES); // 256 bit
// Generate the Message Authentication Code
$mac = sodium_crypto_auth($msg, $key);
// Altering $mac or $msg, verification will fail
echo sodium_crypto_auth_verify($mac, $msg, $key) ? 'Success' : 'Error';
HMAC-SHA512

EXAMPLE3:EXAMPLE3:
SENDINGSECRETMESSAGESSENDINGSECRETMESSAGES

PUBLIC-KEYENCRYPTIONPUBLIC-KEYENCRYPTION
Note: it provides con dentiality, integrity and non-repudiation
Algorithms: to encrypt, for MAC, and for key exchange
$aliceKeypair = sodium_crypto_box_keypair();
$alicePublicKey = sodium_crypto_box_publickey($aliceKeypair);
$aliceSecretKey = sodium_crypto_box_secretkey($aliceKeypair);
$bobKeypair = sodium_crypto_box_keypair();
$bobPublicKey = sodium_crypto_box_publickey($bobKeypair); // 32 bytes
$bobSecretKey = sodium_crypto_box_secretkey($bobKeypair); // 32 bytes
$msg = 'Hi Bob, this is Alice!';
$nonce = random_bytes(SODIUM_CRYPTO_BOX_NONCEBYTES); // 24 bytes
$keyEncrypt = $aliceSecretKey . $bobPublicKey;
$ciphertext = sodium_crypto_box($msg, $nonce, $keyEncrypt);
$keyDecrypt = $bobSecretKey . $alicePublicKey;
$plaintext = sodium_crypto_box_open($ciphertext, $nonce, $keyDecrypt);
echo $plaintext === $msg ? 'Success' : 'Error';
XSalsa20 Poly1305 XS25519

EXAMPLE4:EXAMPLE4:
DIGITALSIGNATUREDIGITALSIGNATURE

DIGITALSIGNATUREDIGITALSIGNATURE
Note: the message is not encrypted, signedMsg includes signature + msg
Algorithm:
$keypair = sodium_crypto_sign_keypair();
$publicKey = sodium_crypto_sign_publickey($keypair); // 32 bytes
$secretKey = sodium_crypto_sign_secretkey($keypair); // 64 bytes
$msg = 'This message is from Alice';
// Sign a message
$signedMsg = sodium_crypto_sign($msg, $secretKey);
// Or generate only the signature (detached mode)
$signature = sodium_crypto_sign_detached($msg, $secretKey); // 64 bytes
// Verify the signed message
$original = sodium_crypto_sign_open($signedMsg, $publicKey);
echo $original === $msg ? 'Signed msg ok' : 'Error signed msg';
// Verify the signature
echo sodium_crypto_sign_verify_detached($signature, $msg, $publicKey) ?
'Signature ok' : 'Error signature';
Ed25519

EXAMPLE5:EXAMPLE5:
AES-GCMAES-GCM

AEADAES-256-GCMAEADAES-256-GCM
Note: you need to store also ad and nonce + ciphertext
if (! sodium_crypto_aead_aes256gcm_is_available()) {
throw new Exception("AES-GCM is not supported on this platform");
}
$msg = 'Super secret message!';
$key = random_bytes(SODIUM_CRYPTO_AEAD_AES256GCM_KEYBYTES);
$nonce = random_bytes(SODIUM_CRYPTO_AEAD_AES256GCM_NPUBBYTES);
// AEAD encryption
$ad = 'Additional public data';
$ciphertext = sodium_crypto_aead_aes256gcm_encrypt(
$msg,
$ad,
$nonce,
$key
);
// AEAD decryption
$decrypted = sodium_crypto_aead_aes256gcm_decrypt(
$ciphertext,

EXAMPLE6:EXAMPLE6:
STOREPASSWORDSSAFELYSTOREPASSWORDSSAFELY

ARGON2IARGON2I
An example of Argon2i hash:
$password = 'password';
$hash = sodium_crypto_pwhash_str(
$password,
SODIUM_CRYPTO_PWHASH_OPSLIMIT_INTERACTIVE,
SODIUM_CRYPTO_PWHASH_MEMLIMIT_INTERACTIVE
); // 97 bytes
echo sodium_crypto_pwhash_str_verify($hash, $password) ?
'OK' : 'Error';
$argon2id$v=19$m=65536,t=2,p=1$EF1BpShRmCYHN7ryxlhtBg$zLZO4IWjx3E...

ARGON2INPHP7.2ARGON2INPHP7.2
Comparing with Sodium:
Note: password_hash() is not compatible with sodium_crypto_pwhash_str()
// Argon2i without Sodium
$hash = password_hash($password, PASSWORD_ARGON2I); // 95 bytes
echo password_verify($password, $hash) ? 'OK' : 'Error';
$argon2id$v=19$m=65536,t=2,p=1$EF1BpShRmCYH... // 97 bytes, Sodium
$argon2i$v=19$m=1024,t=2,p=2$Y3pweEtMdS82SG... // 95 bytes, PHP

EXAMPLE7:EXAMPLE7:
DERIVEAKEYFROMAUSER'SPASSWORDDERIVEAKEYFROMAUSER'SPASSWORD

PASSWORDAREBADPASSWORDAREBAD
Not random
Predictable (most of the time)
Only a subset of ASCII codes (typically vs )
Never use it as encryption/authentication key!
Use KDF to derive a key from a password
68 256

DERIVEAKEYUSINGARGON2IDERIVEAKEYUSINGARGON2I
Example: generating a binary key of 32 bytes
Note: you need to store also the salt to generate the same key from password
$salt = random_bytes(SODIUM_CRYPTO_PWHASH_SALTBYTES);
$key = sodium_crypto_pwhash(
32,
$password,
$salt,
SODIUM_CRYPTO_PWHASH_OPSLIMIT_INTERACTIVE,
SODIUM_CRYPTO_PWHASH_MEMLIMIT_INTERACTIVE
);

UTILITYINSODIUMUTILITYINSODIUM
Wiping Sensitive Data from Memory:
Hex2bin / Bin2Hex:
Constant-time string comparison:
sodium_memzero(&$secret)
sodium_hex2bin(string $hex, string $ignore = '
sodium_bin2hex(string $bin)
sodium_compare(string $str1, string $str2)

REFERENCESREFERENCES
D.J. Bernstein, T.Lange, and P.Schwabe, ,
Lecture Notes in Computer Science 7533, Springer, 2012. ISBN 978-3-642-33480-1
Daniel J. Bernstein,
OpenDNS Security Research, , March 6, 2013
D.A. Osvik, A.Shamir, E.Tromer, , Lecture
Notes in Computer Science, vol 3860. Springer, 2006
Anthony Ferrara, , 2014
Eric Sesterhenn, , 2017
Angela Raucher, ,
Synopsys
Willy Raedy, , Full Stack Academy of Code
Scott Arciszewski, , Paragonie, 2017
The security impact of a new cryptographic library
Cryptography in NaCl
Introducing Sodium, a new cryptographic library
Cache Attacks and Countermeasures: the Case of AES
It's All About Time
Benchmarking memcmp() for timing attacks
Protecting Against Side-Channel Attacks with an Ultra-Low Power Processor
Elliptic Curve Cryptography Tutorial
Libsodium Quick Reference

THANKS!THANKS!
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