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# ShamirSharedSecret - Reference Documentation

## Index of Methods

- ShamirSharedSecret() constructor
- addShare()
- reconstructSecret()
- getPrime()
- trimSecret()
- createShares()

## Constructor

### Prototype

ShamirSharedSecret(ByteString prime)

ShamirSharedSecret(Number bits)

### Description

Create an instance to generate or reconstruct a shared secret

### Arguments

Type | Name | Description
--- | --- | ---
`ByteString` | prime | The prime to be used
`Number` | bits | The number of bits for the randomly generated prime

### Exceptions

Name | Value | Description
--- | --- | ---
GPError | GPError.ARGUMENTS_MISSING | Too few arguments in call
GPError | GPError.INVALID_ARGUMENTS | Too many arguments in call
GPError | GPError.INVALID_TYPE | Type of argument is invalid for call

### Example

    var prime = new ByteString("e25cb644c99928ff", HEX);
    var sss = new ShamirSharedSecret(prime);

## addShare()

### Prototype

addShare(Number id, ByteString share)

### Description

Add the share identified by id.

### Arguments

Type | Name | Description
--- | --- | ---
`Number` | id | The id for the share
`ByteString` | share | The share value

### Return

`` |

### Exceptions

Name | Value | Description
--- | --- | ---
GPError | GPError.INVALID_ARGUMENTS | Too many arguments in call

### Example

    var share = [
    	new ByteString("dabd6f8a03d16d54", HEX),
    	new ByteString("62d50d9144316251", HEX),
    	new ByteString("cd4961dd4e2a804d", HEX)
    ];

    var sss = new ShamirSharedSecret(prime);
    sss.addShare(1, share[0]);
    sss.addShare(2, share[1]);

## reconstructSecret()

### Prototype

ByteString reconstructSecret()

### Description

Reconstruct the shared secret from previously added shares.

### Return

`ByteString` | The recovered secret

### Exceptions

Name | Value | Description
--- | --- | ---
GPError | GPError.INVALID_ARGUMENTS | Too many arguments in call

### Example

    var s = sss.reconstructSecret();
    // print(s);
    var ref = new ByteString("70491B3DF9D84F58", HEX);
    assert(s.equals(ref));

## getPrime()

### Prototype

ByteString getPrime()

### Description

Return the prime generated or set in the constructor.

### Return

`ByteString` | The prime

### Exceptions

Name | Value | Description
--- | --- | ---
GPError | GPError.INVALID_ARGUMENTS | Too many arguments in call

### Example

    var sss = new ShamirSharedSecret(64);
    var prime = sss.getPrime();
    print("Prime " + prime);

## trimSecret()

### Prototype

ByteString trimSecret(ByteString secret)

### Description

Ensure that the secret is smaller than the prime using a modulo operation.

### Return

`ByteString` | The trimmed secret

### Exceptions

Name | Value | Description
--- | --- | ---
GPError | GPError.INVALID_ARGUMENTS | Too many arguments in call

### Example

    var secret = crypto.generateRandom(9);
    print("Secret (raw)  " + secret);

    secret = sss.trimSecret(secret);
    print("Secret (trim) " + secret);

## createShares()

### Prototype

ByteString[] createShares(ByteString secret, Number threshold, Number shares)

### Description

Create the shares for a given secret. The numeric value of the secret must be smaller than the prime.

### Arguments

Type | Name | Description
--- | --- | ---
`ByteString` | secret | The secret to split. Must be smaller than the prime
`Number` | threshold | The number of shares required to reconstruct
`Number` | shares | The total number of shares.

### Return

`ByteString[]` | An array containing the shares

### Exceptions

Name | Value | Description
--- | --- | ---
GPError | GPError.INVALID_ARGUMENTS | Too many arguments in call

### Example

    var sss = new ShamirSharedSecret(prime);
    var shares = sss.createShares(secret, 2, 3);

    for (var i = 0; i < shares.length; i++) {
    	print("Id " + (i + 1) + " : " + shares[i]);
    }

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