## Summary
Fixes incorrect JWK "d" field length for exported elliptic curve private
keys. The "d" field is now correctly padded to ensure RFC 7518
compliance.
## Problem
When exporting EC private keys to JWK format, the "d" field would
sometimes be shorter than required by RFC 7518 because
`convertToBytes()` doesn't pad the result when the BIGNUM has leading
zeros. This caused incompatibility with Chrome's strict validation,
though Node.js and Firefox would accept the malformed keys.
Expected lengths per RFC 7518:
- P-256: 32 bytes → 43 base64url characters
- P-384: 48 bytes → 64 base64url characters
- P-521: 66 bytes → 88 base64url characters
## Solution
Changed `src/bun.js/bindings/webcrypto/CryptoKeyECOpenSSL.cpp:420` to
use `convertToBytesExpand(privateKey, keySizeInBytes)` instead of
`convertToBytes(privateKey)`, ensuring the private key is padded with
leading zeros when necessary. This matches the behavior already used for
the x and y public key coordinates.
## Test plan
- ✅ Added regression test in `test/regression/issue/24399.test.ts` that
generates multiple keys for each curve and verifies correct "d" field
length
- ✅ Test fails with `USE_SYSTEM_BUN=1 bun test` (reproduces the bug)
- ✅ Test passes with `bun bd test` (verifies the fix)
- ✅ Existing crypto tests pass
Fixes#24399🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
