openssl/openssl

`openssl cms -decrypt -stream` support

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#26,372 opened on Jan 10, 2025

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help wantedtriaged: feature

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Description

openssl cms -encrypt -stream is supported and may produce very large files. That's very good.

Unfortunately, current code that decrypts the result of such encryption loads the whole file into memory. It's inefficient, slow, and sometimes is a blocker for large encrypted files.

I think, streaming decryption (and signature verification in another use case) should be supported.

As a suggestion, if source is a plain file, fadvice() should be used if possible, in order not to pollute pagecache.

Here #26274 I figured out, that -stream is silently ignored on decryption and streaming decryption seems is not implemented at all.

Contributor guide

Research direction
Study the existing CMS encryption streaming implementation and use BIO chains to implement decryption streaming; avoid loading entire file into memory.
Tech stack
c
Domain
cryptography
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
COpenSSL internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40