feat(client/v2/offchain): sign and verify file

client/v2/CHANGELOG.md

@@ -40,6 +40,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### Features
 
+* [#18626](https://github.com/cosmos/cosmos-sdk/pull/18626) Support for off-chain signing and verification of a file.
 * [#18461](https://github.com/cosmos/cosmos-sdk/pull/18461) Support governance proposals.
 
 ### API Breaking Changes

client/v2/README.md

@@ -209,6 +209,63 @@ For example, here is how the SDK does it for `cometbft` gRPC commands:
 https://github.com/cosmos/cosmos-sdk/blob/main/client/grpc/cmtservice/autocli.go#L52-L71
 ```
 
+## Off-Chain
+
+Off-chain functionalities allow you to sign and verify files with two commands:
+ + `sign-file` for signing a file.
+ + `verify-file` for verifying a previously signed file.
+
+Signing a file will result in a Tx with a `MsgSignArbitraryData` as described in the [Off-chain CIP](https://github.com/cosmos/cips/blob/main/cips/cip-X.md).
+
+### Sign a file
+
+To sign a file `sign-file` command offers some helpful flags:
+```text
+      --encoding string          Choose an encoding method for the file content to be added as msg data (no-encoding|base64|hex) (default "no-encoding")
+      --indent string            Choose an indent for the tx (default "  ")
+      --notEmitUnpopulated       Don't show unpopulated fields in the tx
+      --output string            Choose an output format for the tx (json|text (default "json")
+      --output-document string   The document will be written to the given file instead of STDOUT
+```
+
+The `encoding` flag lets you choose how the contents of the file should be encoded. For example:
+ + `simd off-chain sign-file alice myFile.json`
+   + ```json
+      {
+        "@type":  "/offchain.MsgSignArbitraryData",
+        "appDomain":  "simd",
+        "signer":  "cosmos1x33fy6rusfprkntvjsfregss7rvsvyy4lkwrqu",
+        "data":  "Hello World!\n"
+      }
+     ```
+ + `simd off-chain sign-file alice myFile.json --encoding base64`
+   + ```json
+      {
+        "@type":  "/offchain.MsgSignArbitraryData",
+        "appDomain":  "simd",
+        "signer":  "cosmos1x33fy6rusfprkntvjsfregss7rvsvyy4lkwrqu",
+        "data":  "SGVsbG8gV29ybGQhCg=="
+      }
+     ```
++ `simd off-chain sign-file alice myFile.json --encoding hex`
+  + ```json
+        {
+          "@type":  "/offchain.MsgSignArbitraryData",
+          "appDomain":  "simd",
+          "signer":  "cosmos1x33fy6rusfprkntvjsfregss7rvsvyy4lkwrqu",
+          "data":  "48656c6c6f20576f726c64210a"
+        }
+       ```
+
+### Verify a file
+
+To verify a file only the key name used and the previously signed file are needed.
+simd off-chain verify-file alice signedFile.json
+```text
+➜ simd off-chain verify-file alice signedFile.json
+Verification OK!
+```
+
 ## Summary
 
 `autocli` lets you generate CLI to your Cosmos SDK-based applications without any cobra boilerplate. It allows you to easily generate CLI commands and flags from your protobuf messages, and provides many options for customising the behavior of your CLI application.

client/v2/internal/offchain/msgSignArbitraryData.proto

@@ -0,0 +1,20 @@
+syntax = "proto3";
+
+package offchain;
+
+import "cosmos_proto/cosmos.proto";
+import "cosmos/msg/v1/msg.proto";
+import "amino/amino.proto";
+
+// MsgSignArbitraryData defines an arbitrary, general-purpose, off-chain message
+message MsgSignArbitraryData {
+  option (amino.name) = "offchain/MsgSignArbitraryData";
+  option (cosmos.msg.v1.signer) = "signer";
+  // AppDomain is the application requesting off-chain message signing
+  string app_domain = 1;
+  // Signer is the sdk.AccAddress of the message signer
+  string signer = 2 [(cosmos_proto.scalar) = "cosmos.AddressString"];
+  // Data represents the raw bytes of the content that is signed (text, json, etc)
+  string data = 3;
+}
+