substrate-suri-ffi

C FFI library for deriving sr25519 keypairs from Substrate SURI strings. Drop the prebuilt .dll/.so into your Unreal Engine, Unity, or any C/C++ project to sign Substrate extrinsics without embedding a Rust toolchain.

Prebuilt Binaries

dist/
  substrate_suri_ffi.h              # C header
  win64/
    substrate_suri_ffi.dll          # Windows x86_64 (1.7 MB)
    substrate_suri_ffi.lib          # Static lib for MSVC linking
  linux-x86_64/
    libsubstrate_suri_ffi.so        # Linux x86_64 (749 KB)
    libsubstrate_suri_ffi.a         # Static lib

API

#include "substrate_suri_ffi.h"

// Derive 32-byte public key from SURI
int32_t substrate_suri_public_key(const char* suri, uint8_t* out_public_32);

// Derive full keypair (64-byte secret + 32-byte public)
int32_t substrate_suri_keypair(const char* suri, uint8_t* out_secret_64, uint8_t* out_public_32);

// Sign a message with sr25519
int32_t substrate_suri_sign(const char* suri, const uint8_t* msg, uint32_t msg_len, uint8_t* out_sig_64);

// Verify an sr25519 signature
int32_t substrate_suri_verify(const uint8_t* public_32, const uint8_t* msg, uint32_t msg_len, const uint8_t* sig_64);

// Human-readable error message
int32_t substrate_suri_error_message(int32_t error_code, char* out_buf, uint32_t buf_len);

All functions return 0 on success, negative error code on failure.

SURI Examples

SURI	Description
//Alice	Well-known dev account
//Charlie	Well-known dev account
bottom drive obey lake curtain smoke basket hold race lonely fit walk	12-word mnemonic
<mnemonic>//hard/soft	Mnemonic with derivation path

Unreal Engine Integration

1. Copy substrate_suri_ffi.dll to YourPlugin/ThirdParty/SubstrateSuri/bin/Win64/
2. Copy substrate_suri_ffi.h to YourPlugin/ThirdParty/SubstrateSuri/include/
3. In your .Build.cs:

   string ThirdPartyPath = Path.Combine(ModuleDirectory, "..", "ThirdParty", "SubstrateSuri");
   PublicIncludePaths.Add(Path.Combine(ThirdPartyPath, "include"));
   PublicAdditionalLibraries.Add(Path.Combine(ThirdPartyPath, "bin", "Win64", "substrate_suri_ffi.lib"));
   RuntimeDependencies.Add("$(BinaryOutputDir)/substrate_suri_ffi.dll",
       Path.Combine(ThirdPartyPath, "bin", "Win64", "substrate_suri_ffi.dll"));

4. Call from C++:

   #include "substrate_suri_ffi.h"
   
   uint8_t PublicKey[32];
   int32_t Result = substrate_suri_public_key("//Charlie", PublicKey);
   if (Result != 0) { /* handle error */ }

Building from Source

# Linux
cargo build --release
# Output: target/release/libsubstrate_suri_ffi.so

# Windows (cross-compile from Linux)
rustup target add x86_64-pc-windows-gnu
cargo build --release --target x86_64-pc-windows-gnu
# Output: target/x86_64-pc-windows-gnu/release/substrate_suri_ffi.dll

# Windows (native MSVC)
cargo build --release --target x86_64-pc-windows-msvc
# Output: target/x86_64-pc-windows-msvc/release/substrate_suri_ffi.dll

# Android
rustup target add aarch64-linux-android
cargo build --release --target aarch64-linux-android
# Output: target/aarch64-linux-android/release/libsubstrate_suri_ffi.so

Requires Rust 1.70+ and sp-core v34.

Tests

cargo test

6 tests: key derivation (Alice, Charlie), keypair extraction, sign+verify round-trip, bad SURI rejection, invalid signature detection.

License

MIT