tx: sign hash of code rather than full code blob

.changelog/unreleased/improvements/807-smaller-signing.md

@@ -0,0 +1,2 @@
+- Sign over the hash of code rather than code in transaction signing.
+  ([#807](https://github.com/anoma/namada/pull/807))

shared/src/proto/types.rs

@@ -127,6 +127,100 @@ where
     }
 }
 
+/// A Tx with its code replaced by a hash salted with the Borsh
+/// serialized timestamp of the transaction. This structure will almost
+/// certainly be smaller than a Tx, yet in the usual cases it contains
+/// enough information to confirm that the Tx is as intended and make a
+/// non-malleable signature.
+#[derive(
+    Clone, Debug, PartialEq, BorshSerialize, BorshDeserialize, BorshSchema, Hash,
+)]
+pub struct SigningTx {
+    pub code_hash: [u8; 32],
+    pub data: Option<Vec<u8>>,
+    pub timestamp: DateTimeUtc,
+}
+
+impl SigningTx {
+    pub fn hash(&self) -> [u8; 32] {
+        let timestamp = Some(self.timestamp.into());
+        let mut bytes = vec![];
+        types::Tx {
+            code: self.code_hash.to_vec(),
+            data: self.data.clone(),
+            timestamp,
+        }
+        .encode(&mut bytes)
+        .expect("encoding a transaction failed");
+        hash_tx(&bytes).0
+    }
+
+    /// Sign a transaction using [`SignedTxData`].
+    pub fn sign(self, keypair: &common::SecretKey) -> Self {
+        let to_sign = self.hash();
+        let sig = common::SigScheme::sign(keypair, to_sign);
+        let signed = SignedTxData {
+            data: self.data,
+            sig,
+        }
+        .try_to_vec()
+        .expect("Encoding transaction data shouldn't fail");
+        SigningTx {
+            code_hash: self.code_hash,
+            data: Some(signed),
+            timestamp: self.timestamp,
+        }
+    }
+
+    /// Verify that the transaction has been signed by the secret key
+    /// counterpart of the given public key.
+    pub fn verify_sig(
+        &self,
+        pk: &common::PublicKey,
+        sig: &common::Signature,
+    ) -> std::result::Result<(), VerifySigError> {
+        // Try to get the transaction data from decoded `SignedTxData`
+        let tx_data = self.data.clone().ok_or(VerifySigError::MissingData)?;
+        let signed_tx_data = SignedTxData::try_from_slice(&tx_data[..])
+            .expect("Decoding transaction data shouldn't fail");
+        let data = signed_tx_data.data;
+        let tx = SigningTx {
+            code_hash: self.code_hash,
+            data,
+            timestamp: self.timestamp,
+        };
+        let signed_data = tx.hash();
+        common::SigScheme::verify_signature_raw(pk, &signed_data, sig)
+    }
+
+    /// Expand this reduced Tx using the supplied code only if the the code
+    /// hashes to the stored code hash
+    pub fn expand(self, code: Vec<u8>) -> Option<Tx> {
+        if hash_tx(&code).0 == self.code_hash {
+            Some(Tx {
+                code,
+                data: self.data,
+                timestamp: self.timestamp,
+            })
+        } else {
+            None
+        }
+    }
+}
+
+impl From<Tx> for SigningTx {
+    fn from(tx: Tx) -> SigningTx {
+        SigningTx {
+            code_hash: hash_tx(&tx.code).0,
+            data: tx.data,
+            timestamp: tx.timestamp,
+        }
+    }
+}
+
+/// A SigningTx but with the full code embedded. This structure will almost
+/// certainly be bigger than SigningTxs and contains enough information to
+/// execute the transaction.
 #[derive(
     Clone, Debug, PartialEq, BorshSerialize, BorshDeserialize, BorshSchema, Hash,
 )]
@@ -261,28 +355,20 @@ impl Tx {
     }
 
     pub fn hash(&self) -> [u8; 32] {
-        hash_tx(&self.to_bytes()).0
+        SigningTx::from(self.clone()).hash()
     }
 
     pub fn code_hash(&self) -> [u8; 32] {
-        hash_tx(&self.code).0
+        SigningTx::from(self.clone()).code_hash
     }
 
     /// Sign a transaction using [`SignedTxData`].
     pub fn sign(self, keypair: &common::SecretKey) -> Self {
-        let to_sign = self.hash();
-        let sig = common::SigScheme::sign(keypair, to_sign);
-        let signed = SignedTxData {
-            data: self.data,
-            sig,
-        }
-        .try_to_vec()
-        .expect("Encoding transaction data shouldn't fail");
-        Tx {
-            code: self.code,
-            data: Some(signed),
-            timestamp: self.timestamp,
-        }
+        let code = self.code.clone();
+        SigningTx::from(self)
+            .sign(keypair)
+            .expand(code)
+            .expect("code hashes to unexpected value")
     }
 
     /// Verify that the transaction has been signed by the secret key
@@ -292,18 +378,7 @@ impl Tx {
         pk: &common::PublicKey,
         sig: &common::Signature,
     ) -> std::result::Result<(), VerifySigError> {
-        // Try to get the transaction data from decoded `SignedTxData`
-        let tx_data = self.data.clone().ok_or(VerifySigError::MissingData)?;
-        let signed_tx_data = SignedTxData::try_from_slice(&tx_data[..])
-            .expect("Decoding transaction data shouldn't fail");
-        let data = signed_tx_data.data;
-        let tx = Tx {
-            code: self.code.clone(),
-            data,
-            timestamp: self.timestamp,
-        };
-        let signed_data = tx.hash();
-        common::SigScheme::verify_signature_raw(pk, &signed_data, sig)
+        SigningTx::from(self.clone()).verify_sig(pk, sig)
     }
 }
 

wasm/checksums.json

@@ -1,20 +1,20 @@
 {
-    "tx_bond.wasm": "tx_bond.27f2a447889b931c9ac5e175fbc19f124277cd677d83e1624a5467ac43f3551f.wasm",
-    "tx_change_validator_commission.wasm": "tx_change_validator_commission.df16d46f67c5fe02392f87cf3dbfabb728f4be506fb2461af051e2a17efff383.wasm",
-    "tx_ibc.wasm": "tx_ibc.494dda55184d02f1d0061e99f642683b916d6eada6ade291e3be26d0c1385be9.wasm",
-    "tx_init_account.wasm": "tx_init_account.67805cd6d6b9280d1b907d7a2eec3f3b740c9863aebf4ed655b387c455f44922.wasm",
-    "tx_init_proposal.wasm": "tx_init_proposal.1011afeb69c550014b4f8f989458af326258fc08b4ddb60067b7485b07eb2a55.wasm",
-    "tx_init_validator.wasm": "tx_init_validator.0df6c8985b40993b3ad62b2cde6a76aecaeb6282b6916a0c98e44deac38c5089.wasm",
-    "tx_reveal_pk.wasm": "tx_reveal_pk.c5d4ddb9a9ce2b5e1f2c3c063e36549a535d383a73e569476c218548392d5ccc.wasm",
-    "tx_transfer.wasm": "tx_transfer.52f882ed5abe72b456e490e035a09ad220141fc04dd8606e3300c7bc4971aea6.wasm",
-    "tx_unbond.wasm": "tx_unbond.6b1d54cf6978b55e2318deb1a2a37fd77d810dbabefc0a7422ca21c0ac3f6a61.wasm",
-    "tx_update_vp.wasm": "tx_update_vp.98cea95bd9191b65d90188c733514843333ae1c653c03c2a317fc641116ff01f.wasm",
-    "tx_vote_proposal.wasm": "tx_vote_proposal.d5da43dbe86aaa10ddd509cd451a762c52803af3e196b08cced3cee16feb63a7.wasm",
-    "tx_withdraw.wasm": "tx_withdraw.b6a713a643f6e5b7a4a8263881c4df7d50656990111ccd02e6596ca5575dbe8b.wasm",
-    "vp_implicit.wasm": "vp_implicit.5cfa9136bd218e9dcc44276265454a3dcebe81d0a11f2a090d354e3463098481.wasm",
-    "vp_masp.wasm": "vp_masp.00b2bfeb805847bc5f825b8ec632b6eae77cd64a9c5553b87599ba0756489fa4.wasm",
-    "vp_testnet_faucet.wasm": "vp_testnet_faucet.d4f1f3f54348630ee8d805ac44e6799da193f3a1353728fcafe7634cfc3ca0e4.wasm",
-    "vp_token.wasm": "vp_token.3f887a991f03a6c447a88307d8e04c569162e126e6016740dd884724bc7b3969.wasm",
-    "vp_user.wasm": "vp_user.2f63cc6f131760edd0975d41c081288921e76d82883699bbfcc8005980c98aca.wasm",
-    "vp_validator.wasm": "vp_validator.32701a8c9c331a3814e72bcd406b7ae9de3f250e820ac729145841e2ff802123.wasm"
+    "tx_bond.wasm": "tx_bond.7235131a24027f3f1b7a23fc6ebd9d5627ba70ae28517eb9124078892aec551c.wasm",
+    "tx_change_validator_commission.wasm": "tx_change_validator_commission.39cc08bafbe7f2b51646605352453fce591da52c4eb4a1d18d4f42a92cde1d04.wasm",
+    "tx_ibc.wasm": "tx_ibc.260a6a4ef24753abb7466f2d3ca77d3e56a814732dd4ad36e6b78c07ee862c6d.wasm",
+    "tx_init_account.wasm": "tx_init_account.867a6ecb57949686dd00123492b34cfa79981dc74448057d6d993a3a0b2559bd.wasm",
+    "tx_init_proposal.wasm": "tx_init_proposal.e63ed208992c36648d62b2ad0b05103e153cc829bd87b31d3fab48ce990fac09.wasm",
+    "tx_init_validator.wasm": "tx_init_validator.54569d151871eab0ba2ff31691dcea4f37dacc48463b84c0df35d1623c97f108.wasm",
+    "tx_reveal_pk.wasm": "tx_reveal_pk.d981228b6193ef1eef36c7f87813c91db445b33d7cf785efb3c55611fb78dc3c.wasm",
+    "tx_transfer.wasm": "tx_transfer.6433f99399995ef2dda9c96279e2ba4ebcfa0b08c4e4bb01f2759b6d226978f7.wasm",
+    "tx_unbond.wasm": "tx_unbond.33dc68a3cc75e68fdc8d313b6433a5c7e81e7664f5b8456c9f13e5211a4d4422.wasm",
+    "tx_update_vp.wasm": "tx_update_vp.4be5efb701dcf603cd51f0f4e5a25db5262d085f8b17c12e377b4b4f8b11716c.wasm",
+    "tx_vote_proposal.wasm": "tx_vote_proposal.e721c21aa031613afd43fc92d9330ab383438644b1af1f74c7d99bad2ebea0c7.wasm",
+    "tx_withdraw.wasm": "tx_withdraw.1b89806a37e9974092f97ed6dd67b464d5d7cfbf63b7bb3197342145c8eeefd4.wasm",
+    "vp_implicit.wasm": "vp_implicit.8ba8a6af407a1a18778d65d10c04c5384dba1d31d00bc69b529786380af6cdf0.wasm",
+    "vp_masp.wasm": "vp_masp.9c4e6207009fc716f08c9c65abe9e15dc63fcad97805dfa62f3a9924211fb78f.wasm",
+    "vp_testnet_faucet.wasm": "vp_testnet_faucet.0916d238eacd22e77cd8bfbb3580e89a3f5d9c90857257616023d0f25f7063a2.wasm",
+    "vp_token.wasm": "vp_token.37b2e0d7c7286ad7f3b69fa09e62d226d7e636b8749333826a4ef1648dee2128.wasm",
+    "vp_user.wasm": "vp_user.f34a7feb62f7da2b304b00656e89a948df222a4991765d501677c4f16a1cb1b6.wasm",
+    "vp_validator.wasm": "vp_validator.588c11066f49dd6c9a53b703873d883e7398006e8ede21ea184b348767ec5a7f.wasm"
 }