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Dylan M. Taylor
a1e9eb8a31
Moved from MailCraft's crates/assuan at a44a45013d1c. The code is unchanged apart from the crate name and doc wording that named the app. The S-expression reader, socket-file reader, limits and all 60 tests come with it.
28 lines
1.6 KiB
Markdown
28 lines
1.6 KiB
Markdown
# craft-assuan
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The Assuan protocol and gpg-agent's operations, without sockets.
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OpenPGP private keys stay in GnuPG (on disk or on a smartcard) and are used through gpg-agent,
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which asks for the PIN or passphrase in its own pinentry. This crate speaks to the agent over any
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`Read + Write` stream the caller opened.
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- **`Client`**: Assuan's line framing (lines of at most `MAX_LINE` bytes, percent-escaping), the
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server's `OK`, `ERR`, `S`, `D`, `INQUIRE` and `#` lines, and answers to an inquiry (`D` … `END`,
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or `CAN`).
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- **`GpgAgent`**: whether a key is there (`HAVEKEY`, `KEYINFO`, `READKEY`), signing a digest
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(`SIGKEY`, `SETHASH`, `PKSIGN`; SHA-256, SHA-384 and SHA-512 only), decrypting a session key
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(`SETKEY`, `PKDECRYPT`), and the hints that let the agent's pinentry show on the owner's screen.
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- **`sexp`**: a bounded reader and writer of canonical S-expressions, the form the agent hands
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keys, signatures and session keys over in.
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- **`socket_file`**: the two kinds of file that may stand where the agent's socket is named: a
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redirect, and (on Windows) the loopback port and nonce of Assuan's socket emulation.
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Finding the agent and opening the socket is the caller's. Everything the agent sends is treated
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as hostile: lines, data, status lines, inquiries and S-expressions are capped (`MAX_LINE`,
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`MAX_DATA`, `MAX_LINES`, `MAX_STATUS`, `MAX_INQUIRIES`, `MAX_INQUIRY_DATA`, `MAX_KEYS`), and
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nothing here panics on junk. A session key that comes back is wiped from memory when it is
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dropped and is never shown by `Debug`.
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Written from the public documentation of the Assuan protocol and of gpg-agent's commands. Moved
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from MailCraft's `mailcraft-assuan`.
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