Clarify field limits in EthereumSignTx

protob/messages.proto

@@ -592,6 +592,7 @@ message TxAck {
 /**
  * Request: Ask device to sign transaction
  * All fields are optional from the protocol's point of view. Each field defaults to value `0` if missing.
+ * Note: the first at most 1024 bytes of data MUST be transmitted as part of this message.
  * @next PassphraseRequest
  * @next PinMatrixRequest
  * @next EthereumTxRequest
@@ -599,11 +600,11 @@ message TxAck {
  */
 message EthereumSignTx {
 	repeated uint32 address_n = 1;			// BIP-32 path to derive the key from master node
-	optional bytes nonce = 2;			// 256 bit unsigned big endian
-	optional bytes gas_price = 3;			// 256 bit unsigned big endian (in wei)
-	optional bytes gas_limit = 4;			// 256 bit unsigned big endian
+	optional bytes nonce = 2;			// <=256 bit unsigned big endian
+	optional bytes gas_price = 3;			// <=256 bit unsigned big endian (in wei)
+	optional bytes gas_limit = 4;			// <=256 bit unsigned big endian
 	optional bytes to = 5;				// 160 bit address hash
-	optional bytes value = 6;			// 256 bit unsigned big endian (in wei)
+	optional bytes value = 6;			// <=256 bit unsigned big endian (in wei)
 	optional bytes data_initial_chunk = 7;		// The initial data chunk (<= 1024 bytes)
 	optional uint32 data_length = 8;		// Length of transaction payload
 }
@@ -611,15 +612,15 @@ message EthereumSignTx {
 /**
  * Response: Device asks for more data from transaction payload, or returns the signature.
  * If data_length is set, device awaits that many more bytes of payload.
- * Otherwise, the signature_* fields contain the computed transaction signature.
+ * Otherwise, the signature_* fields contain the computed transaction signature. All three fields will be present.
  * @prev EthereumSignTx
  * @next EthereumTxAck
  */
 message EthereumTxRequest {
-	optional uint32 data_length = 1;		// Number of bytes being requested
+	optional uint32 data_length = 1;		// Number of bytes being requested (<= 1024)
 	optional uint32 signature_v = 2;		// Computed signature (recovery parameter, limited to 27 or 28)
-	optional bytes signature_r = 3;			// Computed signature
-	optional bytes signature_s = 4;			// Computed signature
+	optional bytes signature_r = 3;			// Computed signature R component (256 bit)
+	optional bytes signature_s = 4;			// Computed signature S component (256 bit)
 }
 
 /**
@@ -628,7 +629,7 @@ message EthereumTxRequest {
  * @next EthereumTxRequest
  */
 message EthereumTxAck {
-	optional bytes data_chunk = 1;			// Bytes from transaction payload
+	optional bytes data_chunk = 1;			// Bytes from transaction payload (<= 1024 bytes)
 }
 
 ///////////////////////