http://sovereign.i2p/verifiable-credential.html
The Sovereign Project provides sign/verify messages that make it easy to issue, accept and verify credentials/contracts. A typical Sovereign Project cryptographic signature looks like: {"json":"2.0","method":"digital_signature","params":{"signature":"SigV29RG2mPBcSpxU2pYXFZxGjxWgFRG9XEjPZKtiiMqan1GDAz75bPYaFHbar4AFacJuG9Cua8cHCckadJcUfBX2GeKW", "id":"82UYxMCsE94HMo929REPqsjgLb5LjomLL9i58YJf1ufB5HCciizthp4gYAV2wi1A6wVVqhsPHPUCvL4pd4Sir3RFQy5mT9r","data":"This is a test!