ssh-key: add SshSig signing example (#167)

Complements #166 with an example for how to produce signatures

ssh-key/src/private.rs

@@ -275,6 +275,40 @@ impl PrivateKey {
     ///
     /// See [PROTOCOL.sshsig] for more information.
     ///
+    /// # Usage
+    ///
+    /// See also: [`PublicKey::verify`].
+    ///
+    #[cfg_attr(feature = "ed25519", doc = "```")]
+    #[cfg_attr(not(feature = "ed25519"), doc = "```ignore")]
+    /// # fn main() -> Result<(), ssh_key::Error> {
+    /// use ssh_key::{PrivateKey, HashAlg, SshSig};
+    ///
+    /// // Message to be signed.
+    /// let message = b"testing";
+    ///
+    /// // Example domain/namespace used for the message.
+    /// let namespace = "example";
+    ///
+    /// // Private key to use when computing the signature.
+    /// // WARNING: don't actually hardcode private keys in source code!!!
+    /// let encoded_private_key = r#"
+    /// -----BEGIN OPENSSH PRIVATE KEY-----
+    /// b3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtzc2gtZW
+    /// QyNTUxOQAAACCzPq7zfqLffKoBDe/eo04kH2XxtSmk9D7RQyf1xUqrYgAAAJgAIAxdACAM
+    /// XQAAAAtzc2gtZWQyNTUxOQAAACCzPq7zfqLffKoBDe/eo04kH2XxtSmk9D7RQyf1xUqrYg
+    /// AAAEC2BsIi0QwW2uFscKTUUXNHLsYX4FxlaSDSblbAj7WR7bM+rvN+ot98qgEN796jTiQf
+    /// ZfG1KaT0PtFDJ/XFSqtiAAAAEHVzZXJAZXhhbXBsZS5jb20BAgMEBQ==
+    /// -----END OPENSSH PRIVATE KEY-----
+    /// "#;
+    ///
+    /// let private_key = encoded_private_key.parse::<PrivateKey>()?;
+    /// let signature = private_key.sign(namespace, HashAlg::default(), message)?;
+    /// // assert!(private_key.public_key().verify(namespace, message, &signature).is_ok());
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
     /// [PROTOCOL.sshsig]: https://cvsweb.openbsd.org/src/usr.bin/ssh/PROTOCOL.sshsig?annotate=HEAD
     #[cfg(feature = "alloc")]
     pub fn sign(&self, namespace: &str, hash_alg: HashAlg, msg: &[u8]) -> Result<SshSig> {

ssh-key/src/public.rs

@@ -50,6 +50,9 @@ use serde::{de, ser, Deserialize, Serialize};
 #[cfg(feature = "std")]
 use std::{fs, path::Path};
 
+#[cfg(doc)]
+use crate::PrivateKey;
+
 /// SSH public key.
 ///
 /// # OpenSSH encoding
@@ -172,6 +175,8 @@ impl PublicKey {
     ///
     /// # Usage
     ///
+    /// See also: [`PrivateKey::sign`].
+    ///
     #[cfg_attr(feature = "ed25519", doc = "```")]
     #[cfg_attr(not(feature = "ed25519"), doc = "```ignore")]
     /// # fn main() -> Result<(), ssh_key::Error> {
@@ -184,17 +189,19 @@ impl PublicKey {
     /// let namespace = "example";
     ///
     /// // Public key which computed the signature.
-    /// let public_key_str = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAILM+rvN+ot98qgEN796jTiQfZfG1KaT0PtFDJ/XFSqti user@example.com";
+    /// let encoded_public_key = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAILM+rvN+ot98qgEN796jTiQfZfG1KaT0PtFDJ/XFSqti user@example.com";
     ///
     /// // Example signature to be verified.
-    /// let signature_str = "-----BEGIN SSH SIGNATURE-----
+    /// let signature_str = r#"
+    /// -----BEGIN SSH SIGNATURE-----
     /// U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgsz6u836i33yqAQ3v3qNOJB9l8b
     /// UppPQ+0UMn9cVKq2IAAAAHZXhhbXBsZQAAAAAAAAAGc2hhNTEyAAAAUwAAAAtzc2gtZWQy
     /// NTUxOQAAAEBPEav+tMGNnox4MuzM7rlHyVBajCn8B0kAyiOWwPKprNsG3i6X+voz/WCSik
     /// /FowYwqhgCABUJSvRX3AERVBUP
-    /// -----END SSH SIGNATURE-----";
+    /// -----END SSH SIGNATURE-----
+    /// "#;
     ///
-    /// let public_key = public_key_str.parse::<PublicKey>()?;
+    /// let public_key = encoded_public_key.parse::<PublicKey>()?;
     /// let signature = signature_str.parse::<SshSig>()?;
     /// public_key.verify(namespace, message, &signature)?;
     /// # Ok(())

ssh-key/src/sshsig.rs

@@ -10,7 +10,7 @@ use encoding::{
 use signature::Verifier;
 
 #[cfg(doc)]
-use crate::PublicKey;
+use crate::{PrivateKey, PublicKey};
 
 type Version = u32;
 
@@ -28,7 +28,7 @@ type Version = u32;
 ///
 /// # Usage
 ///
-/// See [`SshSig::sign`] and [`PublicKey::verify`] for usage information.
+/// See [`PrivateKey::sign`] and [`PublicKey::verify`] for usage information.
 ///
 /// [PROTOCOL.sshsig]: https://cvsweb.openbsd.org/src/usr.bin/ssh/PROTOCOL.sshsig?annotate=HEAD
 #[derive(Clone, Debug, Eq, PartialEq)]
@@ -96,6 +96,8 @@ impl SshSig {
     }
 
     /// Sign the given message with the provided signing key.
+    ///
+    /// See also: [`PrivateKey::sign`].
     pub fn sign<S: SigningKey>(
         signing_key: &S,
         namespace: &str,