eth_sign_tx: integrate address case feature to go library

see : BitBoxSwiss/bitbox02-firmware@055bda6#diff-3c37126459943046256cdb0d98c78832b5630e54b1d56aff57a8fac56d2964bc

For ETH signing legacy and EIP1559 transactions, the BitBox02 device
shows confirmation screens for recipient and amount. For recipient, the
device was previously showing the address in mixed case according to
EIP-55, no matter the case user has entered. This created confusions
among the users.

That is why not the go library detects the case of the recipient address
useer inputted and sends this case information to BitBox02 device, which
will in turn show the recipient address in the same case that it got
from the library.

Signed-off-by: asi345 <inanata15@gmail.com>

Author: asi345

api/firmware/eth.go

@@ -141,6 +141,17 @@ func (device *Device) handleSignerNonceCommitment(response *messages.ETHResponse
 	return signature, nil
 }
 
+func identifyCase(hexString string) messages.ETHAddressCase {
+	switch {
+	case strings.ToUpper(hexString) == hexString:
+		return messages.ETHAddressCase_ETH_ADDRESS_CASE_UPPER
+	case strings.ToLower(hexString) == hexString:
+		return messages.ETHAddressCase_ETH_ADDRESS_CASE_LOWER
+	default:
+		return messages.ETHAddressCase_ETH_ADDRESS_CASE_MIXED
+	}
+}
+
 // ETHSign signs an ethereum transaction. It returns a 65 byte signature (R, S, and 1 byte recID).
 func (device *Device) ETHSign(
 	chainID uint64,
@@ -168,6 +179,10 @@ func (device *Device) ETHSign(
 	if err != nil {
 		return nil, err
 	}
+
+	recipient_hex := hex.EncodeToString(recipient[:])
+	address_case := identifyCase(recipient_hex)
+
 	request := &messages.ETHRequest{
 		Request: &messages.ETHRequest_Sign{
 			Sign: &messages.ETHSignRequest{
@@ -181,6 +196,7 @@ func (device *Device) ETHSign(
 				Value:               value.Bytes(),
 				Data:                data,
 				HostNonceCommitment: hostNonceCommitment,
+				AddressCase:         address_case,
 			},
 		},
 	}
@@ -224,6 +240,9 @@ func (device *Device) ETHSignEIP1559(
 		return nil, err
 	}
 
+	recipient_hex := hex.EncodeToString(recipient[:])
+	address_case := identifyCase(recipient_hex)
+
 	request := &messages.ETHRequest{
 		Request: &messages.ETHRequest_SignEip1559{
 			SignEip1559: &messages.ETHSignEIP1559Request{
@@ -237,6 +256,7 @@ func (device *Device) ETHSignEIP1559(
 				Value:                value.Bytes(),
 				Data:                 data,
 				HostNonceCommitment:  hostNonceCommitment,
+				AddressCase:          address_case,
 			},
 		},
 	}