Add method to bls::PublicKey for short ID

beacon_chain/utils/bls/Cargo.toml

@@ -7,4 +7,5 @@ edition = "2018"
 [dependencies]
 bls-aggregates = { git = "https://github.com/sigp/signature-schemes" }
 hashing = { path = "../hashing" }
+hex = "0.3"
 ssz = { path = "../ssz" }

beacon_chain/utils/bls/src/public_key.rs

@@ -1,5 +1,6 @@
 use super::SecretKey;
 use bls_aggregates::PublicKey as RawPublicKey;
+use hex::encode as hex_encode;
 use ssz::{decode_ssz_list, ssz_encode, Decodable, DecodeError, Encodable, SszStream};
 use std::hash::{Hash, Hasher};
 
@@ -19,6 +20,15 @@ impl PublicKey {
     pub fn as_raw(&self) -> &RawPublicKey {
         &self.0
     }
+
+    /// Returns the last 6 bytes of the SSZ encoding of the public key, as a hex string.
+    ///
+    /// Useful for providing a short identifier to the user.
+    pub fn concatenated_hex_id(&self) -> String {
+        let bytes = ssz_encode(self);
+        let end_bytes = &bytes[bytes.len().saturating_sub(6)..bytes.len()];
+        hex_encode(end_bytes)
+    }
 }
 
 impl Encodable for PublicKey {