# eth_ecrecover · Rell standard library · Chromia Docs (concept)

> pure function eth_ ecrecover(r: byte_array , s: byte_array , rec_id: integer , data_hash: byte_array ): byte_array Compute an Ethererum public key from a s

Source: https://docs.chromia.com/pages/rell-stdlib/-rell-system-library/crypto/eth_ecrecover/

FUNCTION

# eth\_ecrecover

```signature
pure function eth_ecrecover(r: byte_array, s: byte_array, rec_id: integer, data_hash: byte_array): byte_array
```

Compute an Ethererum public key from a signature and a hash.

Similar to Solidity's `ecrecover()`, though differs in that:

* This function takes `rec_id`, rather than `v`, where `rec_id == v - 27`.
* The parameter order is different.
* This function returns a 64-byte public key, not a 20-byte address. An address can be obtained by
  taking the last 20 bytes of the `keccak256()` digest of the returned public key, e.g.:

Rell

```
val address: byte_array = keccak256(eth_ecrecover(...)).sub(44);
```

The signature (consisting of the `r`, `s` and `rec_id` components) will typically be obtained with a
procedure equivalent to `eth_sign(data_hash, privkey)`, where `privkey` and `pubkey` form a keypair
(`pubkey` being returned form this method).

The signature component `rec_id` is an *adjusted* recovery identifier, equivalent to Ethereum's
recovery identifier (usually denoted as `v`) **minus 27**, i.e. `rec_id == v - 27`.

The given 32-byte array `data_hash` is typically a cryptographic hash obtained from a larger data
structure using a hashing function such as `hash()`, `sha256()` or `keccak256()`.

### Example

The following is a Node.js script which uses `ecrecover()` (the equivalent to
`crypto.eth_ecrecover()`) from the Ethereum Web3 library:

JavaScript

```
const Web3 = require('web3');
const web3 = new Web3();
var r = '0xcf722a47bcf1da61967ccc6405e31db4d37bce153255a6937e5cceb222caead0';
var s = '0xcf722a47bcf1da61967ccc6405e31db4d37bce153255a6937e5cceb222caead0';
var h = '0x53d7b11e61a8059aa4bc3248d24b2936436c9796dfe7f18e414c181004f79427';
var v = '0x1c';
var address = web3.eth.accounts.recover({'r':r,'s':s,'messageHash':h,'v':v});
console.log(address); // prints 0x5b0c087542D5C1E66Df0041e179c4201675B1614
```

An equivalent script in Rell is as follows:

Rell

```
val r = x'cf722a47bcf1da61967ccc6405e31db4d37bce153255a6937e5cceb222caead0';
val s = x'cf722a47bcf1da61967ccc6405e31db4d37bce153255a6937e5cceb222caead0';
val h = x'53d7b11e61a8059aa4bc3248d24b2936436c9796dfe7f18e414c181004f79427';
val v = 0x1c;
val pubkey = eth_ecrecover(r, s, v - 27, h);
val address = keccak256(pubkey).sub(12);
print(address); // prints 0x5b0c087542d5c1e66df0041e179c4201675b1614
```

Note that in the Rell script, `v` is an integer, while in the Node.js script it is an `0x`-prefixed
hexadecimal string.

**Parameters**

* **r** — the first component of the Ethereum signature
* **s** — the second component of the Ethereum signature
* **rec\_id** — the recovery identifier, normally `0` or `1`
* **data\_hash** — the original (unsigned) 32-byte array

**Returns**

a 64-byte public key

Since 0.10.6

[View this page on docs.chromia.com](https://docs.chromia.com/pages/rell-stdlib/-rell%20-system%20-library/crypto/eth_ecrecover.html)Generated API reference, mirrored from the live docs