PHP 7.2: The First Programming Language to Add Modern Cryptography to its Standard Library

Last week, the voting phase closed on an RFC to add libsodium to PHP 7.2. The result was unanimous (37 in favor, 0 against).

When version 7.2 releases at the end of the year, PHP will be the first programming language to adopt modern cryptography in its standard library.

What is Modern Cryptography?

A cryptography library can be said to be modern if it meets two requirements:

1. Uses fast primitives designed to resist side-channel cryptanalysis (e.g. timing leaks, padding oracles).
2. Exposes a high-level API that is simple and secure-by-default.

Secure Primitives

If you implement public key encryption and digital signatures in OpenSSL and Golang, you're forced to choose between RSA and NIST ECC. Neither is a good choice.

• Very few developers can get RSA right:
  • e = d = 1
  • Invites developers to implement RSA-ECB
  • PKCS1v1.5 padding
• NIST's Elliptic Curve Cryptography
  • Invalid curve attacks, which gives away your secret key via the Chinese Remainder Theorem if an attacker submits (x, y) coordinates that aren't on the curve
  • In the case of ECDSA (before RFC 6979), repeated k values for ECDSA signatures gave away your secret keys
  • NIST Curves aren't rigid

Modern cryptography requires the use of secure primitives. For public key crpytography, that means the primitives outlined in RFC 7748 and RFC 8032. For symmetric cryptography, that means using authenticated encryption at all times.

NIST curves (P-256, etc.) do not qualify as modern cryptography (although their presence in a library doesn't automatically disqualify either).

Libsodium's primitives include:

• X25519 (Elliptic Curve Diffie-Hellman over Curve25519)
• Ed25519 (Edwards-curve Digital Signature Algorithm over Curve25519)
• Xsalsa20poly1305 (authenticated symmetric-key encryption that performs well in software and doesn't have cache-timing vulnerabilities like software AES)
• BLAKE2 (based on the SHA3 finalist that performs faster than MD5 in software but is more secure than SHA256)
• Argon2 (password hashing and key derivation function)
• SipHash-2-4 (fast hash for hash tables and similar data structures)
• ChaCha20-Poly1305 (authenticated encryption with associated data)

But you'll likely not need to worry about these details, because it also provides a...

Simple and Secure High-Level API

To facilitate public-key encryption in libsodium, you just need the following:

// Some example variables:
$alice_ecdh_secret = 
    "\x69\xf2\x08\x41\x2d\x8d\xd5\xdb\x9d\x0c\x6d\x18\x51\x2e\x86\xf0" . 
    "\xec\x75\x66\x5a\xb8\x41\x37\x2d\x57\xb0\x42\xb2\x7e\xf8\x9d\x8c";
$bob_ecdh_public =
    "\xe8\x98\x0c\x86\xe0\x32\xf1\xeb\x29\x75\x05\x2e\x8d\x65\xbd\xdd" .
    "\x15\xc3\xb5\x96\x41\x17\x4e\xc9\x67\x8a\x53\x78\x9d\x92\xc7\x54";
$message_keypair = sodium_crypto_box_keypair_from_secretkey_and_publickey(
    $alice_ecdh_secret,
    $bob_ecdh_public
);
$plaintext = "This is a secret message for your eyes only.";
$nonce = random_bytes(24);

// And now for the actual public-key encryption step:
$ciphertext = sodium_crypto_box($plaintext, $nonce, $message_keypair);

To decrypt a message:

$received = sodium_crypto_box_open(
    $received_ciphertext, 
    $received_nonce, 
    $message_keypair
);

What does this mean for me?

If you develop in PHP and can upgrade to 7.2 when it comes out, you get to enjoy modern cryptography as a part of the language itself. It will now be possible to design software that uses Ed25519 digital signatures (e.g. for automatic security updates) without requiring users to install an optional PHP extension.

I hate PHP, there's no way it's more secure than $favoriteLanguage

This has come up a bunch in response to my tweet announcing the RFC passing. However, most of the languages that were proposed as being ahead of PHP on this issue weren't.

Here are the facts:

Go 1.8 will use X25519 and ChaCha20-Poly1305 in its TLS stack, but it doesn't offer modern application-layer cryptography in its standard library. Which means if you want to use modern TLS, you can, but if you want to encrypt data at rest, you have to either go outside the standard library or use 90's era public-key cryptography.

Most other programming languages (Ruby, Erlang, Node.js) still only offer OpenSSL, which invites developers to (mis)use RSA, encrypt using AES in ECB mode, and never authenticate their ciphertexts. Furthermore, many of these languages still use OpenSSL's userspace PRNG and don't expose a sane API for accessing the operating system's CSPRNG. (PHP solved this in 7.0.)

No matter how you feel about PHP, the reality is that PHP is the first programming language to commit to modern cryptography in its standard library, coming in version 7.2.0.

If you're a passionate language evangelist, the best thing to do now is to strive for second-to-market. I'm excited to see everyone abandon the fossils of RSA and foot-bullety ECDSA.