openssl_pkey_new() fails for EC keys on OpenSSL 3.6 - incorrectly requires private_key_bits #21083
Description
Description
When using openssl_pkey_new() to generate EC keys with OpenSSL 3.6.0, the function incorrectly requires
private_key_bits even though this parameter is not relevant for elliptic curve keys (the key size is determined
by the curve itself).
The workaround requires setting private_key_bits to 384, which is semantically incorrect for a 256-bit curve
like prime256v1. Setting it to 256 (the actual curve size) still fails.
The OpenSSL CLI generates EC keys without issues (openssl ecparam -name prime256v1 -genkey -noout), suggesting
this is a PHP bindings issue.
Environment: PHP 8.5.2, OpenSSL 3.6.0
Possible cause
OpenSSL 3.6 requires C-99 compilers (no longer ANSI-C), which changes integer behavior and sizes. Additionally,
OpenSSL 3.6 modified EC keygen error handling.
The private_key_bits parameter should not apply to EC keys at all - the curve name (e.g., prime256v1)
implicitly defines the key size. It appears PHP's OpenSSL bindings incorrectly validate private_key_bits for EC
keys when linked against OpenSSL 3.6.
This same error has been reported in other projects:
- https://community.librenms.org/t/new-install-openssl-pkey-new-private-key-length-must-be-at-least-384-bits-conf
igured-to-0/22396 - passport:install error (openssl_pkey_new(): private key length is too short; it needs to be at least 384 bits, not 0) laravel/passport#757
References
- openssl_pkey_new() fails on OpenSSL 3.6 - missing private_key_bits parameter web-push-libs/web-push-php#445
- https://github.com/openssl/openssl/blob/openssl-3.6.0/CHANGES.md
- Switch to C99 without the features that became optional in C11 openssl/technical-policies#50 (C-99 requirement)
The following code:
<?php
$key = openssl_pkey_new([
'curve_name' => 'prime256v1',
'private_key_type' => OPENSSL_KEYTYPE_EC,
]);
var_dump($key);
var_dump(openssl_error_string());
Resulted in this output:
bool(false)
string(63) "Private key length must be at least 384 bits, configured to 0"
But I expected this output instead:
object(OpenSSLAsymmetricKey)#1 (0) {}
bool(false)PHP Version
PHP 8.5.2 (cli) (built: Jan 17 2026 23:04:39) (NTS clang 15.0.0)
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Operating System
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