Encrypt HTTP uploads with PGP (symmetrically)

The symmetric key (passphrase) is put into the fragment part of the
upload URL. The upload URL is part of the message as a protected header
and in the body payload. If the message is encrypted itself, the
symmetric key is encrypted with the message.

src/pgp.rs

@@ -10,6 +10,7 @@ use pgp::composed::{
     SignedPublicSubKey, SignedSecretKey, SubkeyParamsBuilder,
 };
 use pgp::crypto::{HashAlgorithm, SymmetricKeyAlgorithm};
+use pgp::ser::Serialize;
 use pgp::types::{
     CompressionAlgorithm, KeyTrait, Mpi, PublicKeyTrait, SecretKeyTrait, StringToKey,
 };
@@ -322,8 +323,22 @@ pub async fn pk_decrypt(
     Ok(content)
 }
 
-/// Symmetric encryption.
+/// Symmetric encryption with armored base64 text output.
 pub async fn symm_encrypt(passphrase: &str, plain: &[u8]) -> Result<String> {
+    let message = symm_encrypt_to_message(passphrase, plain).await?;
+    let encoded_msg = message.to_armored_string(None)?;
+    Ok(encoded_msg)
+}
+
+/// Symmetric encryption with binary output.
+pub async fn symm_encrypt_bytes(passphrase: &str, plain: &[u8]) -> Result<Vec<u8>> {
+    let message = symm_encrypt_to_message(passphrase, plain).await?;
+    let mut buf = Vec::new();
+    message.to_writer(&mut buf)?;
+    Ok(buf)
+}
+
+async fn symm_encrypt_to_message(passphrase: &str, plain: &[u8]) -> Result<Message> {
     let lit_msg = Message::new_literal_bytes("", plain);
     let passphrase = passphrase.to_string();
 
@@ -332,10 +347,7 @@ pub async fn symm_encrypt(passphrase: &str, plain: &[u8]) -> Result<String> {
         let s2k = StringToKey::new_default(&mut rng);
         let msg =
             lit_msg.encrypt_with_password(&mut rng, s2k, Default::default(), || passphrase)?;
-
-        let encoded_msg = msg.to_armored_string(None)?;
-
-        Ok(encoded_msg)
+        Ok(msg)
     })
     .await
 }

src/upload.rs

@@ -1,12 +1,26 @@
 use crate::context::Context;
 use crate::error::{bail, Result};
+use crate::pgp::{symm_decrypt, symm_encrypt_bytes};
+use async_std::fs;
 use async_std::path::PathBuf;
 use rand::Rng;
+use std::io::Cursor;
+use url::Url;
 
 /// Upload file to a HTTP upload endpoint.
-pub async fn upload_file(_context: &Context, url: String, filepath: PathBuf) -> Result<String> {
-    // TODO: Use tokens for upload, encrypt file with PGP.
-    let response = surf::put(url).body_file(filepath)?.await;
+pub async fn upload_file(
+    context: &Context,
+    url: impl AsRef<str>,
+    filepath: PathBuf,
+) -> Result<String> {
+    let (passphrase, url) = parse_upload_url(url)?;
+
+    let content = fs::read(filepath).await?;
+    let encrypted = symm_encrypt_bytes(&passphrase, &content).await?;
+
+    // TODO: Use tokens for upload.
+    info!(context, "uploading encrypted file to {}", &url);
+    let response = surf::put(url).body_bytes(encrypted).await;
     if let Err(err) = response {
         bail!("Upload failed: {}", err);
     }
@@ -17,16 +31,59 @@ pub async fn upload_file(_context: &Context, url: String, filepath: PathBuf) ->
     }
 }
 
+/// Download and decrypt a file from a HTTP endpoint.
+/// TODO: Use this.
+#[allow(dead_code)]
+pub async fn download_file(context: &Context, url: String) -> Result<Vec<u8>> {
+    let (passphrase, url) = parse_upload_url(url)?;
+    info!(context, "downloading file from {}", &url);
+    let response = surf::get(url).recv_bytes().await;
+    if let Err(err) = response {
+        bail!("Download failed: {}", err);
+    }
+    let reader = Cursor::new(response.unwrap());
+    let decrypted = symm_decrypt(&passphrase, reader).await?;
+    Ok(decrypted)
+}
+
+/// Parse a URL from a string and take out the hash fragment.
+fn parse_upload_url(url: impl AsRef<str>) -> Result<(String, Url)> {
+    let mut url = url::Url::parse(url.as_ref())?;
+    let passphrase = url.fragment();
+    if passphrase.is_none() {
+        bail!("Missing passphrase for upload URL");
+    }
+    let passphrase = passphrase.unwrap().to_string();
+    url.set_fragment(None);
+    Ok((passphrase, url))
+}
+
 /// Generate a random URL based on the provided endpoint.
-pub fn generate_upload_url(_context: &Context, endpoint: String) -> String {
+pub fn generate_upload_url(_context: &Context, mut endpoint: String) -> String {
+    // equals at least 16 random bytes (base32 takes 160% of binary size).
+    const FILENAME_LEN: usize = 26;
+    // equals at least 32 random bytes.
+    const PASSPHRASE_LEN: usize = 52;
+
+    if endpoint.chars().last() == Some('/') {
+        endpoint.pop();
+    }
+    let passphrase = generate_token_string(PASSPHRASE_LEN);
+    let filename = generate_token_string(FILENAME_LEN);
+    format!("{}/{}#{}", endpoint, filename, passphrase)
+}
+
+/// Generate a random string encoded in base32.
+/// Len is the desired string length of the result.
+/// TODO: There's likely better methods to create random tokens.
+pub fn generate_token_string(len: usize) -> String {
     const CROCKFORD_ALPHABET: &[u8] = b"0123456789abcdefghjkmnpqrstvwxyz";
-    const FILENAME_LEN: usize = 27;
     let mut rng = rand::thread_rng();
-    let filename: String = (0..FILENAME_LEN)
+    let token: String = (0..len)
         .map(|_| {
             let idx = rng.gen_range(0, CROCKFORD_ALPHABET.len());
             CROCKFORD_ALPHABET[idx] as char
         })
         .collect();
-    format!("{}{}", endpoint, filename)
+    token
 }