> ## Documentation Index
> Fetch the complete documentation index at: https://docs.qu.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# SigningKey

A **SigningKey** provides high-level access to the elliptic curve cryptography (ECC) operations and key management.

## Constructors

### new SigningKey()

```ts theme={null}
new SigningKey(privateKey): SigningKey
```

Creates a new **SigningKey** for `privateKey`.

#### Parameters

| Parameter    | Type                                               |
| :----------- | :------------------------------------------------- |
| `privateKey` | [`BytesLike`](/sdk/content/type-aliases/BytesLike) |

#### Returns

[`SigningKey`](/sdk/content/classes/SigningKey)

#### Source

[crypto/signing-key.ts:26](https://github.com/dominant-strategies/quais.js/blob/c1c12d43f9d34c6baad2b0542bd6d0acd6fefcbf/src/crypto/signing-key.ts#L26)

## Accessors

### compressedPublicKey

```ts theme={null}
get compressedPublicKey(): string
```

The compressed public key.

This will always begin with either the prefix `0x02` or `0x03` and be 68 characters long (the `0x` prefix and 33
hexadecimal nibbles)

#### Returns

`string`

#### Source

[crypto/signing-key.ts:54](https://github.com/dominant-strategies/quais.js/blob/c1c12d43f9d34c6baad2b0542bd6d0acd6fefcbf/src/crypto/signing-key.ts#L54)

***

### privateKey

```ts theme={null}
get privateKey(): string
```

The private key.

#### Returns

`string`

#### Source

[crypto/signing-key.ts:34](https://github.com/dominant-strategies/quais.js/blob/c1c12d43f9d34c6baad2b0542bd6d0acd6fefcbf/src/crypto/signing-key.ts#L34)

***

### publicKey

```ts theme={null}
get publicKey(): string
```

The uncompressed public key.

This will always begin with the prefix `0x04` and be 132 characters long (the `0x` prefix and 130 hexadecimal
nibbles).

#### Returns

`string`

#### Source

[crypto/signing-key.ts:44](https://github.com/dominant-strategies/quais.js/blob/c1c12d43f9d34c6baad2b0542bd6d0acd6fefcbf/src/crypto/signing-key.ts#L44)

## Methods

### computeSharedSecret()

```ts theme={null}
computeSharedSecret(other): string
```

Returns the [ECDH](https://en.wikipedia.org/wiki/Elliptic-curve_Diffie-Hellman) shared secret between this
private key and the `other` key.

The `other` key may be any type of key, a raw public key, a compressed/uncompressed pubic key or aprivate key.

Best practice is usually to use a cryptographic hash on the returned value before using it as a symetric secret.

#### Parameters

| Parameter | Type                                               | Description                                      |
| :-------- | :------------------------------------------------- | :----------------------------------------------- |
| `other`   | [`BytesLike`](/sdk/content/type-aliases/BytesLike) | The other key to compute the shared secret with. |

#### Returns

`string`

The shared secret.

#### Example

```ts theme={null}
sign1 = new SigningKey(id('some-secret-1'));
sign2 = new SigningKey(id('some-secret-2'));

// Notice that privA.computeSharedSecret(pubB)...
sign1.computeSharedSecret(sign2.publicKey);

// ...is equal to privB.computeSharedSecret(pubA).
sign2.computeSharedSecret(sign1.publicKey);
```

#### Source

[crypto/signing-key.ts:103](https://github.com/dominant-strategies/quais.js/blob/c1c12d43f9d34c6baad2b0542bd6d0acd6fefcbf/src/crypto/signing-key.ts#L103)

***

### sign()

```ts theme={null}
sign(digest): Signature
```

Return the signature of the signed `digest`.

#### Parameters

| Parameter | Type                                               | Description       |
| :-------- | :------------------------------------------------- | :---------------- |
| `digest`  | [`BytesLike`](/sdk/content/type-aliases/BytesLike) | The data to sign. |

#### Returns

[`Signature`](/sdk/content/classes/Signature)

The signature of the data.

#### Throws

If the digest is not 32 bytes long.

#### Source

[crypto/signing-key.ts:65](https://github.com/dominant-strategies/quais.js/blob/c1c12d43f9d34c6baad2b0542bd6d0acd6fefcbf/src/crypto/signing-key.ts#L65)

***

### addPoints()

```ts theme={null}
static addPoints(
   p0, 
   p1, 
   compressed?): string
```

Returns the point resulting from adding the ellipic curve points `p0` and `p1`.

This is not a common function most developers should require, but can be useful for certain privacy-specific
techniques.

For example, it is used by [**QuaiHDWallet**](../classes/QuaiHDWallet) to compute child addresses from parent
public keys and chain codes.

#### Parameters

| Parameter     | Type                                               | Description                                  |
| :------------ | :------------------------------------------------- | :------------------------------------------- |
| `p0`          | [`BytesLike`](/sdk/content/type-aliases/BytesLike) | The first point to add.                      |
| `p1`          | [`BytesLike`](/sdk/content/type-aliases/BytesLike) | The second point to add.                     |
| `compressed`? | `boolean`                                          | Whether to return the compressed public key. |

#### Returns

`string`

The sum of the points.

#### Source

[crypto/signing-key.ts:205](https://github.com/dominant-strategies/quais.js/blob/c1c12d43f9d34c6baad2b0542bd6d0acd6fefcbf/src/crypto/signing-key.ts#L205)

***

### computePublicKey()

```ts theme={null}
static computePublicKey(key, compressed?): string
```

Compute the public key for `key`, optionally `compressed`.

The `key` may be any type of key, a raw public key, a compressed/uncompressed public key or private key.

#### Parameters

| Parameter     | Type                                               | Description                                  |
| :------------ | :------------------------------------------------- | :------------------------------------------- |
| `key`         | [`BytesLike`](/sdk/content/type-aliases/BytesLike) | The key to compute the public key for.       |
| `compressed`? | `boolean`                                          | Whether to return the compressed public key. |

#### Returns

`string`

The public key.

#### Example

```ts theme={null}
sign = new SigningKey(id('some-secret'));

// Compute the uncompressed public key for a private key
SigningKey.computePublicKey(sign.privateKey);

// Compute the compressed public key for a private key
SigningKey.computePublicKey(sign.privateKey, true);

// Compute the uncompressed public key
SigningKey.computePublicKey(sign.publicKey, false);

// Compute the Compressed a public key
SigningKey.computePublicKey(sign.publicKey, true);
```

#### Source

[crypto/signing-key.ts:135](https://github.com/dominant-strategies/quais.js/blob/c1c12d43f9d34c6baad2b0542bd6d0acd6fefcbf/src/crypto/signing-key.ts#L135)

***

### recoverPublicKey()

```ts theme={null}
static recoverPublicKey(digest, signature): string
```

Returns the public key for the private key which produced the `signature` for the given `digest`.

#### Parameters

| Parameter   | Type                                                       | Description                |
| :---------- | :--------------------------------------------------------- | :------------------------- |
| `digest`    | [`BytesLike`](/sdk/content/type-aliases/BytesLike)         | The data that was signed.  |
| `signature` | [`SignatureLike`](/sdk/content/type-aliases/SignatureLike) | The signature of the data. |

#### Returns

`string`

The public key.

#### Example

```ts theme={null}
key = new SigningKey(id('some-secret'));
digest = id('hello world');
sig = key.sign(digest);

// Notice the signer public key...
key.publicKey;

// ...is equal to the recovered public key
SigningKey.recoverPublicKey(digest, sig);
```

#### Source

[crypto/signing-key.ts:177](https://github.com/dominant-strategies/quais.js/blob/c1c12d43f9d34c6baad2b0542bd6d0acd6fefcbf/src/crypto/signing-key.ts#L177)