OCI Request Signer for C

This project provides a C implementation of Oracle Cloud Infrastructure (OCI) request signature, suitable for use in embedded, kernel, or user-space applications. It includes a shared library and an example application demonstrating usage.

Features

• Produces the HTTP Authorization header (key and value) for OCI requests, including the computed signature and all required metadata
• OCI request signing for HTTP requests
• No dynamic memory allocations
• Support for DER format private keys
• Default headers and automatic body hashing based on request method
• Simple API for integration into C projects
• Example usage and tests included
• System header configurability via OCI_SYSTEM_HEADER

Building

Prerequisites

• GCC or compatible C compiler
• pkg-config utility
• OpenSSL for testing and examples
• libcheck for testing

Build Instructions

sudo apt install libssl-dev check

To build the shared library and example application, run:

make

This will produce:

• libocisigner.so: Shared library implementing OCI request signing
• example: Example application using the library

Run Tests

make run-tests

Clean Build Artifacts

make clean

Usage

Private Key Format

This library only accepts RSA private keys in DER format. The private key is stored in a dedicated binary data type (oci_signer_binary_t) to clearly indicate that it contains binary data rather than a string.

If you have a PEM format key, you need to convert it to DER format before using it with this library:

# Convert PEM to DER format
openssl rsa -in private_key.pem -outform DER -out private_key.der

Key ID Format

The library supports two formats for the key_id parameter:

1. Standard format: tenancy/user/fingerprint

   ocid1.tenancy.oc1..aaaaaaaaba3pv6wkcr4jqae5f15p2b2m2yt2j6rx32uzr4h25vqstifsfdsq/ocid1.user.oc1..aaaaaaaat5nvwcna5j6aqzjcaty5eqbb6qt2jvpkanghtgdaqedqw3rynjq/20:3b:97:13:55:1c:5b:0d:d3:37:d8:50:4e:c5:3a:34
   

2. Session token format: ST$<user principal session token>

   ST$aaaaaaaa7tz3aaaaaaaaaymq2maaaaaaabfwiljtdnfgqaaaa
   

System Header Configurability

You can configure the system header used by the library by defining the macro OCI_SYSTEM_HEADER during compilation. This allows integration with custom or platform-specific headers as needed.

Example:

gcc -DOCI_SYSTEM_HEADER='<your_header.h>' ...

Linking

Include the header in your application:

#include "oci_signer.h"

Link against the shared library and OpenSSL:

-L. -locisigner -lssl -lcrypto

Example Usage

The main output of this library is the HTTP Authorization header, which you add to your request:

oci_signer_header_t auth_header;
// ... set up signer parameters ...
oci_signer_sign(&signer_params, &auth_header, buffer_size);
// Now add:
//   Header key:   (char*)auth_header.key.data   // will be "Authorization"
//   Header value: (char*)auth_header.value.data // contains the computed signature and metadata

See example.c for a complete usage demonstration, including examples of how to use custom crypto functions.

Custom Crypto Implementation

For integration with custom environments (like Linux kernel modules), you can provide your own implementations of the required crypto functions:

1. Define OCI_SYSTEM_HEADER to include environment-specific headers instead of standard C library headers
2. Provide custom implementations of the required crypto functions:
   • SHA256 hash function
   • RSA signing function
   • Base64 encoding function

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

This implementation of computing the request authorization header is based on the OCI Go SDK's HTTP signer