Add configurable OAEP hash algorithm#200
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OAEP padding was hardcoded to use SHA-1 for both the label hash and
MGF1 mask generation. Modern compliance standards (NIST SP 800-56B)
and many APIs now require OAEP with SHA-256 or stronger.
Add use_sha{1,224,256,384,512}_oaep_hash() methods that configure the
OAEP hash independently of the signature hash. On OpenSSL 3.x, the
selected hash is passed to EVP_PKEY_CTX via set_rsa_oaep_md and
set_rsa_mgf1_md. On pre-3.x, only SHA-1 is supported (RSA_public_encrypt
hardcodes it); attempting non-SHA1 OAEP croaks with a clear message.
The max plaintext length check now uses the configured OAEP hash
digest size instead of the hardcoded SHA-1 overhead (42 bytes).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
The OAEP overhead is 2*hash_length+2, not a fixed 42 bytes. Document the formula and give examples for SHA-1/SHA-256/SHA-512. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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What
Add
use_sha{1,224,256,384,512}_oaep_hash()methods to configure the hashalgorithm used for OAEP padding, independent of the signature hash.
Why
OAEP was hardcoded to SHA-1 for both the label hash and MGF1. Modern
compliance standards (NIST SP 800-56B Rev. 2) and APIs increasingly
require OAEP with SHA-256 or stronger. Users had no way to satisfy
these requirements without dropping to raw OpenSSL.
How
oaepHashModefield inrsaData(default:NID_sha1for backward compat)rsa_crypt()configuresEVP_PKEY_CTX_set_rsa_oaep_mdandEVP_PKEY_CTX_set_rsa_mgf1_mdwith the selected hashhardcodes SHA-1, no workaround)
check_max_message_length()computes OAEP overhead from the configured hashdigest size instead of the hardcoded 42 bytes
Testing
t/oaep_hash.t: SHA-1/256/512 round-trips, max-lengthboundary checks, hash mismatch detection, pre-3.x guard
🤖 Generated with Claude Code
Quality Report
Changes: 3 files changed, 203 insertions(+), 2 deletions(-)
Code scan: clean
Tests: passed (OK)
Branch hygiene: clean
Generated by Kōan post-mission quality pipeline