feat: Initial implementation

Signed-off-by: Jagoda Ślązak <jslazak@jslazak.com>
2026-09-12 10:23:14 +00:00 · 2026-08-18 12:21:27 +02:00
parent 61261170ad
commit 81b4aecce9
21 changed files with 2870 additions and 0 deletions
@@ -0,0 +1,269 @@
+//! OpenPGP payload checker.
+
+use crate::error;
+use base64::Engine;
+use base64::engine::general_purpose::STANDARD as BASE64_STANDARD;
+
+/// Tries to get the byte `$idx` of the array slice `$payload`.
+///
+/// Returns [`error::Error::TruncatedHeader`] in the outer function, if `$idx` is out of range.
+macro_rules! get_byte {
+    ($payload:expr, $idx:expr) => {
+        *$payload.get($idx).ok_or(error::Error::TruncatedHeader)?
+    };
+}
+
+/// Checks the OpenPGP payload.
+///
+/// OpenPGP payload must consist only of `PKESK` and `SKESK` packets terminated by a single `SEIPD` packet.
+///
+/// Returns `Ok(true)` if OpenPGP payload is correct, `Ok(false)` otherwise.
+///
+/// # Errors
+///
+/// Returns an [`error::Error::TruncatedHeader`] if the OpenPGP packet header is truncated.
+fn check_openpgp_payload(payload: &[u8]) -> Result<bool, error::Error> {
+    let mut i: usize = 0;
+    while i < payload.len() {
+        // Only OpenPGP format is allowed.
+        if (get_byte!(payload, i) & 0xC0) != 0xC0 {
+            log::debug!("check_openpgp_payload: i={i} Not OpenPGP format");
+            return Ok(false);
+        }
+
+        let packet_type_id = get_byte!(payload, i) & 0x3F;
+        i += 1;
+
+        while get_byte!(payload, i) >= 224 && get_byte!(payload, i) < 255 {
+            // Partial body length.
+            let partial_length = 1usize << (get_byte!(payload, i) & 0x1F);
+            i += 1 + partial_length;
+        }
+
+        let body_len: usize;
+        if get_byte!(payload, i) < 192 {
+            // One-octet length.
+            body_len = get_byte!(payload, i) as usize;
+            i += 1;
+        } else if get_byte!(payload, i) < 224 {
+            // Two-octet length.
+            body_len = (((get_byte!(payload, i) as usize) - 192) << 8)
+                + (get_byte!(payload, i + 1) as usize)
+                + 192;
+            i += 2;
+        } else if get_byte!(payload, i) == 255 {
+            // Five-octet length.
+            body_len = ((get_byte!(payload, i + 1) as usize) << 24)
+                | ((get_byte!(payload, i + 2) as usize) << 16)
+                | ((get_byte!(payload, i + 3) as usize) << 8)
+                | (get_byte!(payload, i + 4) as usize);
+            i += 5;
+        } else {
+            // Impossible, partial body length was processed above.
+            log::debug!("check_openpgp_payload: i={i} Invalid body length");
+            return Ok(false);
+        }
+
+        i += body_len;
+
+        if i == payload.len() {
+            // Last packet should be
+            // Symmetrically Encrypted and Integrity Protected Data Packet (SEIPD)
+            //
+            // This is the only place where this function may return `True`.
+            log::debug!(
+                "check_openpgp_payload: i={i} packat_type_id={}",
+                packet_type_id
+            );
+            return Ok(packet_type_id == 18);
+        } else if ![1, 3].contains(&packet_type_id) {
+            // All packets except the last one must be either
+            // Public-Key Encrypted Session Key Packet (PKESK)
+            // or
+            // Symmetric-Key Encrypted Session Key Packet (SKESK)
+            log::debug!(
+                "check_openpgp_payload: i={i} packet_type_id={}",
+                packet_type_id
+            );
+            return Ok(false);
+        }
+    }
+
+    Ok(false)
+}
+
+/// Check the armored PGP message for invalid content.
+///
+/// Returns `true` if the `payload` is a valid PGP message,
+/// `outgoing` informs whether the message is outgoing or incoming
+pub fn check_armored_payload(mut payload: String, outgoing: bool) -> bool {
+    const PREFIX: &str = "-----BEGIN PGP MESSAGE-----\r\n";
+    if !payload.starts_with(PREFIX) {
+        log::debug!("check_armored_payload: Did not find PGP MESSAGE prefix");
+        return false;
+    }
+    payload = payload[PREFIX.len()..].to_string();
+
+    while payload.ends_with("\r\n") {
+        payload.truncate(payload.len() - 2);
+    }
+    const SUFFIX: &str = "-----END PGP MESSAGE-----";
+    if !payload.ends_with(SUFFIX) {
+        log::debug!("check_armored_payload: Did not find PGP MESSAGE suffix");
+        return false;
+    }
+    payload.truncate(payload.len() - SUFFIX.len());
+
+    const VERSION_COMMENT: &str = "Version: ";
+    if payload.starts_with(VERSION_COMMENT) {
+        // Disallow comments in outgoing messages
+        if outgoing {
+            log::debug!("check_armored_payload: Comment found in outgoing message");
+            return false;
+        }
+        // Remove comments from incoming messages
+        if let Some((_, right)) = payload.split_once("\r\n") {
+            payload = right.to_string();
+        }
+    }
+
+    while payload.starts_with("\r\n") {
+        payload = payload[2..].to_string();
+    }
+
+    // Remove CRC24.
+    if let Some((left, _)) = payload.rsplit_once('=') {
+        payload = left.to_string();
+    }
+
+    payload = payload.replace(['\r', '\n'], "");
+    let payload = match BASE64_STANDARD.decode(payload.as_bytes()) {
+        Ok(v) => v,
+        Err(_) => {
+            log::debug!("check_armored_payload: Base64 decoding failed");
+            return false;
+        }
+    };
+
+    check_openpgp_payload(&payload).unwrap_or(false)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use rstest::*;
+
+    #[rstest]
+    #[case::valid(r#"-----BEGIN PGP MESSAGE-----
+
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+=agR5
+-----END PGP MESSAGE-----"#, (true, true))]
+    #[case::with_comment(r#"-----BEGIN PGP MESSAGE-----
+Version: 1
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+=agR5
+-----END PGP MESSAGE-----"#, (false, true))]
+    #[case::invalid_base64(r#"-----BEGIN PGP MESSAGE-----
+
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+=agR5
+-----END PGP MESSAGE-----"#, (false, false))]
+    #[case::invalid_non_pgp_base64(r#"-----BEGIN PGP MESSAGE-----
+
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+=4cf0a3
+-----END PGP MESSAGE-----"#, (false, false))]
+    #[case::invalid_cleartext(r#"-----BEGIN PGP MESSAGE-----
+
+Definitely not base64 encoded PGP message content.
+-----END PGP MESSAGE-----"#, (false, false))]
+    #[case::invalid_no_begin(r#"-----END PGP MESSAGE-----"#, (false, false))]
+    #[case::invalid_no_end(r#"-----BEGIN PGP MESSAGE-----"#, (false, false))]
+    fn test_check_armored_payload(#[case] pgp_message: &str, #[case] expected: (bool, bool)) {
+        let (expected_outgoing, expected_incoming) = expected;
+
+        let result = check_armored_payload(pgp_message.replace('\n', "\r\n").to_string(), true);
+        assert_eq!(result, expected_outgoing);
+
+        let result = check_armored_payload(pgp_message.replace('\n', "\r\n").to_string(), false);
+        assert_eq!(result, expected_incoming);
+    }
+}