Add encryption

- actually encrypt the body of a mail

src/crypto.rs

@@ -4,12 +4,14 @@
 // cryptographic functions
 //
 
+use std::io::Write;
 use std::sync::Arc;
 
 use anyhow;
 use bytes::Bytes;
 use sequoia_openpgp::parse::{PacketParser, PacketParserResult, Parse};
 use sequoia_openpgp::policy::StandardPolicy;
+use sequoia_openpgp::serialize::stream::{Message, Armorer, Encryptor, LiteralWriter};
 use sequoia_openpgp::{Fingerprint, Cert, Packet};
 use sequoia_openpgp::cert::raw::RawCertParser;
 use sequoia_cert_store::{Store, CertStore, LazyCert};
@@ -20,6 +22,7 @@ use wot::{Depth, Path};
 use crate::types::errors::HuskError;
 use crate::types::husk_context::HuskContext;
 use crate::types::introducer::Introducer;
+use crate::types::recipient::Recipient;
 
 pub fn get_local_trust_root(cert_store: &CertStore) -> anyhow::Result<Cert> {
 
@@ -155,6 +158,42 @@ pub fn is_encrypted(body: &Bytes) -> bool {
     false
 }
 
+pub fn encrypt(context: &HuskContext<'_>, body: &Bytes, recipients: &Vec<Recipient>)
+    -> anyhow::Result<Bytes> {
+
+    let mut keys = Vec::new();
+
+    // XXX: handle the case where a certificate misses an encryption subkey
+    for rcpt in recipients {
+        if rcpt.can_encrypt() {
+            for cert in &rcpt.certs {
+                cert.with_policy(&context.policy, None)?
+                    .keys()
+                    .supported()
+                    .alive()
+                    .revoked(false)
+                    .for_transport_encryption()
+                    .for_each(|k| {
+                        keys.push(k);
+                    });
+            }
+        }
+    }
+    if keys.len() > 0 {
+        let mut sink = Vec::new();
+        let message = Message::new(&mut sink);
+        let message = Armorer::new(message).build()?;
+        let message = Encryptor::for_recipients(message, keys).build()?;
+        let mut message = LiteralWriter::new(message).build()?;
+        message.write_all(&body[..])?;
+        message.finalize()?;
+
+        Ok(Bytes::from(sink))
+    } else {
+        Err(HuskError::NoEncryptionKeys.into())
+    }
+}
+
 #[cfg(test)]
 pub mod tests {
    use bytes::Bytes;