Ed25519: Allow signing of >64 byte buffers

[padelsbach]

Found during OpenSSL compat testing

[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #492

Scan targets checked: wolfprovider-src, wolfprovider-bugs
Findings: 3
2 finding(s) posted as inline comments (see file-level comments below)

Required changes (1)

Oversized capacities truncate before signing

File: src/wp_ecx_sig.c:384
Function: wp_ed25519_digest_sign
Category: Incorrect sizeof/type usage

The new oversized-buffer path permits sigSize > UINT32_MAX, then truncates it to word32; capacities whose low 32 bits are below 64 are rejected despite being sufficient. Unlike known #10409, this is post-acceptance truncation.

Related known finding #10409 (similar but distinct): Both affect wp_ed25519_digest_sign and caller-provided signature capacity, but #10409 faults at an exact-64 capacity check, while this finding faults when an already-accepted size_t capacity is narrowed to word32. The root causes and required patches differ: accept capacities >=64 versus avoid post-validation truncation by using the fixed 64-byte signing output capacity.

Suggested fix: Pass ED25519_SIG_SIZE as wolfCrypt's output capacity after validating the caller's effective capacity.
Basis: RFC 8032 §5.1.6 defines an Ed25519 signature as the 64-octet concatenation of R and S.

Referenced code: src/wp_ecx_sig.c:384-387 (4 lines)

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This review was generated automatically by Fenrir. Reported findings require changes before merge.

Fenrir's latest completed scan found no issues; clearing the prior automated change request.

[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #492

Scan targets checked: wolfprovider-src, wolfprovider-bugs

Fenrir result: Approved ✅

No new issues found in the changed files.

Advisory only — this automated result does not count as a GitHub approval.