computeSecret now fails with ERR_CRYPTO_OPERATION_FAILED ("Failed to
compute shared secret") when the exponentiation yields 0, 1 or p - 1,
as Node's OpenSSL derivation does: such a secret is predictable, from a
peer key of small order or a composite modulus. 6708 covers a secret of
1 and of p - 1 (peer keys of order 3 and 6 modulo a 512-bit prime with
p ≡ 1 mod 6) and of 0 (a peer key sharing the factor of a square
modulus).
crypto.createDiffieHellman, crypto.getDiffieHellman and
crypto.createDiffieHellmanGroup return native DiffieHellman and
DiffieHellmanGroup handles backed by mbedTLS bignums. generateKeys,
computeSecret, getPrime, getGenerator, getPublicKey, getPrivateKey,
setPublicKey, setPrivateKey and verifyError follow Node 24.22:
- the modp1, modp2, modp5 and modp14 through modp18 groups, with the
private key widths of Node's OpenSSL 3 path (200 to 400 bits for
modp5 and up, [2, p - 2] for modp1 and modp2);
- explicit primes and generators in every argument form and encoding,
with keys of bits(p) - 2 bits, or below min(2^N, q) when the
parameters equal an OpenSSL named group (RFC 3526, RFC 7919,
RFC 5114);
- generated safe primes with OpenSSL's congruences for the generator;
- verifyError's DH_check bits, computed when it is first read;
- Node's argument, generator, modulus, key range, state and encoding
errors, including the OpenSSL errors' library and reason properties.
Safe-prime generation sieves candidates with the odd primes below a
bound that grows with the prime's length and tests them with
Miller-Rabin rounds over a variable-time Montgomery exponentiation that
only reads public values; key and secret exponentiations stay on
mbedTLS's constant-time path. Primes longer than 8192 bits, property
reads other than verifyError, property writes, Object.prototype methods,
and calls whose output encoding is typed any or matches no @types/node
overload are refused.
The runtime unit scr_dh.c links, with the mbedTLS archive, only into
programs that use DiffieHellman. wasm32-wasi builds refuse it. The ECDH
unit's argument and encoding helpers move to scr_crypto_args.h, which
both units include.
Chris Tate