Implement --list and --list-all commands

Requires a MSRV of 1.44 due to the transitive dependency on bitvec 0.19.

src/p256.rs

@@ -0,0 +1,46 @@
+use bech32::ToBase32;
+use elliptic_curve::sec1::EncodedPoint;
+use p256::NistP256;
+use std::fmt;
+
+use crate::RECIPIENT_PREFIX;
+
+/// Wrapper around a compressed secp256r1 curve point.
+#[derive(Clone)]
+pub struct Recipient(EncodedPoint<NistP256>);
+
+impl fmt::Debug for Recipient {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Recipient({:?})", self.as_bytes())
+    }
+}
+
+impl fmt::Display for Recipient {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(
+            bech32::encode(RECIPIENT_PREFIX, self.as_bytes().to_base32())
+                .expect("HRP is valid")
+                .as_str(),
+        )
+    }
+}
+
+impl Recipient {
+    /// Attempts to parse a valid secp256r1 public key from its SEC-1 encoding.
+    pub(crate) fn from_pubkey(pubkey: EncodedPoint<NistP256>) -> Option<Self> {
+        if pubkey.is_compressed() {
+            if pubkey.decompress().is_some().into() {
+                Some(Recipient(pubkey))
+            } else {
+                None
+            }
+        } else {
+            Some(Recipient(pubkey.compress()))
+        }
+    }
+
+    /// Returns the compressed SEC-1 encoding of this public key.
+    pub(crate) fn as_bytes(&self) -> &[u8] {
+        self.0.as_bytes()
+    }
+}