Skip to content

cipher: fix seeking implementation in the stream cipher wrapper#2052

Merged
newpavlov merged 5 commits intomasterfrom
cipher/fix_stream_seek
Nov 7, 2025
Merged

cipher: fix seeking implementation in the stream cipher wrapper#2052
newpavlov merged 5 commits intomasterfrom
cipher/fix_stream_seek

Conversation

@newpavlov
Copy link
Member

@newpavlov newpavlov commented Oct 29, 2025 •
edited
Loading

The change forbids seeking to the last keystream block and its application. Additionally, unchecked methods added as an escape hatch.

Closes #1808

@newpavlov newpavlov requested a review from tarcieri October 29, 2025 17:43
@tarcieri
Copy link
Member

tarcieri commented Oct 29, 2025

Is this really a fix for #1808? I would think a real fix would make the last keystream block usable

@newpavlov
Copy link
Member Author

newpavlov commented Oct 29, 2025 •
edited
Loading

See my comment in the issue. I spent a significant time trying to implement the last byte approach, but I couldn't get a satisfying solution.

@newpavlov
Copy link
Member Author

newpavlov commented Oct 29, 2025 •
edited
Loading

Another alternative could be to add a special "exhausted" state to the wrapper (either as a separate field, or as part of ReadBuffer), but I don't quite like it either. Adding the field would make all buffered stream cipher implementations bigger (often by more than one byte because of alignment), while modifying ReadBuffer would mean that we need to check the special case every time. Also, I would like to keep the block-buffer code as simple as possible.

Considering that users arguably should not rely on the last keystream block in practice, I am not sure it's worth the trouble.

@newpavlov
Copy link
Member Author

newpavlov commented Nov 7, 2025

@tarcieri
Could you take a look at the updated docs?

tarcieri
tarcieri approved these changes Nov 7, 2025
View reviewed changes
Copy link
Member

@tarcieri tarcieri left a comment

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Docs look good to me

@newpavlov newpavlov merged commit 00a29f8 into master Nov 7, 2025
11 checks passed
@newpavlov newpavlov deleted the cipher/fix_stream_seek branch November 7, 2025 17:03
newpavlov added a commit that referenced this pull request Nov 7, 2025
@newpavlov
cipher: add changelog entry for #2052
9b29d2a
newpavlov added a commit that referenced this pull request Nov 7, 2025
@newpavlov
cipher: add changelog entry for #2052 (#2084)
2cf79f8
@tarcieri tarcieri mentioned this pull request Feb 4, 2026
Merged
tarcieri added a commit that referenced this pull request Feb 4, 2026
@tarcieri
cipher v0.5.0 (#2281)
61a9586 
### Added
- Traits for tweakable block ciphers (#1721)
- Methods for writing keystream (#1907)

### Changed
- Replaced `generic-array` with `hybrid-array` (#1358)
- Rename `BlockCipher*`/`BlockMode*` (#1482)
  - `BlockEncrypt` => `BlockCipherEncrypt`
  - `BlockDecrypt` => `BlockCipherDecrypt`
  - `BlockEncryptMut` => `BlockModeEncrypt`
  - `BlockDecryptMut` => `BlockModeDecrypt`
- Split `BlockBackend` traits into 4 specific traits: (#1636)
  - `BlockCipherEncBackend`
  - `BlockCipherDecBackend`
  - `BlockModeEncBackend`
  - `BlockModeDecBackend`
- Edition changed to 2024 and MSRV bumped to 1.85 (#1759)
- Use `block_buffer::ReadBuffer` in `StreamCipherCoreWrapper` (#1959)
- Re-export of `crypto-common` moved to `cipher::common` (#2237, #2260)
- `crypto-common` dependency bumped to v0.2 (#2276)
- `blobby` requirement bumped to v0.4 (#2147)
- `inout` dependency bumped to v0.2.2 (#2149)

### Fixed
- Bugs in `StreamCipherCoreWrapper` trait implementations (#1421)
- Seeking implementation in the stream cipher wrapper (#2052)

### Removed
- `std` feature (#1691)
- `BlockCipherEncrypt::encrypt_padded*` and
`BlockCipherDecrypt::decrypt_padded*` methods.
Users of the ECB mode should use the `ecb-mode` crate instead. (#2245)
- `AsyncStreamCipher` trait (#2280)
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Reviewers

@tarcieri tarcieri tarcieri approved these changes

Assignees

No one assigned

Labels

None yet

Projects

None yet

Milestone

No milestone

Development

Successfully merging this pull request may close these issues.

cipher: Seeking near the end of the keystream causes try_current_pos to return an error

2 participants

@newpavlov @tarcieri