Hash

The Hash envelope allows storing a document hash on the blockchain. It does not store the document.

By storing the document hash, a user can implement file tampering prevention, allowing other users to be able to validate that the document contents are equal to the original.

Creating a Hash Envelope

Creating a new hash envelope to be stored on chain, can be achieved by adding a specific output object of type hash and add it to the createTransaction outputs argument.

This output type requires the following properties:

Property	Type	Description
data (required)	Uint8Array	Raw file contents. Used to generate the hash. Not stored on chain.
algorithm (required)	String	Hashing algorithm. It can be either 'SHA-256' or 'SHA-512'.
sign (optional)	Boolean	Specify true if the envelope is going to be signed. If this is the case, a signing key needs to be specified. See: key property below.
encrypt(optional)	Boolean	Specify true if the envelope is going to be encrypted. If this is the case, an encryption key needs to be specified. See: key property below.
key (required only if encrypt or signis true)	String | JWK	ES256 Public key of the receiver, either as JWK or as uncompressed hex string
metadata(optional)	Object	Any extra information to store within mintBlue. Not stored on chain.

Example

const data = new Uint8Array(Buffer.from('My file contents'));

const outputs = [
        {
          type: 'hash',
          data: data,
          algorithm: 'SHA-256',
        },
];

// Replace [PROJECT_ID] below with yours.
const { txid, rawtx } = await client.createTransaction({project_id: '[PROJECT_ID]', outputs});

OP_RETURN

The following OP_RETURN arguments are created when a hash envelope is published on a blockchain transaction.

Index	Description	Value
0	Protocol ID	"hash"
1	Envelope	Serialized JWE/JWS
2	Receiver key	Public key of the receiver