diff --git a/README.md b/README.md
index 6d68230..8d7379b 100644
--- a/README.md
+++ b/README.md
@@ -4,3 +4,28 @@ Keccak256 hash function (ethereum version) implemented in [circom](https://githu
 
 **Warning**: WIP, this is an experimental repo.
 
+## Status
+Initial version works, compatible with Ethereum version of Keccak256.
+
+It needs around `150848` (`151k`) constraints. 
+> For context: [Rapidsnark](https://github.com/iden3/rapidsnark) proof generation time:
+> - 1.1M constraints -> 7 seconds (8 CPU)
+> - 128M constraints -> <2min (64 CPU)
+
+## Usage
+- import the lib in the `package.json`:
+```
+"dependencies": {
+	"keccak256-circom": "git+https://github.com/vocdoni/keccak256-circom"
+}
+```
+
+- Usage:
+```
+pragma circom 2.0.0;
+
+include "../node_modules/keccak256-circom/circuits/keccak.circom";
+
+// for a input & output of 32 bytes:
+component main = Keccak(32*8, 32*8);
+```
diff --git a/circuits/keccak.circom b/circuits/keccak.circom
index 61ff39f..f4a1b2f 100644
--- a/circuits/keccak.circom
+++ b/circuits/keccak.circom
@@ -1,3 +1,6 @@
+// Keccak256 hash function (ethereum version).
+// For LICENSE check https://github.com/vocdoni/keccak256-circom/blob/master/LICENSE
+
 pragma circom 2.0.0;
 
 include "./utils.circom";
@@ -164,20 +167,20 @@ template Keccakf() {
     }
 }
 
-template Keccak(nBits) {
-    signal input in[nBits];
-    signal output out[nBits];
+template Keccak(nBitsIn, nBitsOut) {
+    signal input in[nBitsIn];
+    signal output out[nBitsOut];
     var i;
 
-    component f = Final(nBits);
-    for (i=0; i<nBits; i++) {
+    component f = Final(nBitsIn);
+    for (i=0; i<nBitsIn; i++) {
         f.in[i] <== in[i];
     }
-    component squeeze = Squeeze(nBits);
+    component squeeze = Squeeze(nBitsOut);
     for (i=0; i<25*64; i++) {
         squeeze.s[i] <== f.out[i];
     }
-    for (i=0; i<nBits; i++) {
+    for (i=0; i<nBitsOut; i++) {
         out[i] <== squeeze.out[i];
     }
 }
diff --git a/circuits/permutations.circom b/circuits/permutations.circom
index 63d0ab2..e426b71 100644
--- a/circuits/permutations.circom
+++ b/circuits/permutations.circom
@@ -1,3 +1,6 @@
+// Keccak256 hash function (ethereum version).
+// For LICENSE check https://github.com/vocdoni/keccak256-circom/blob/master/LICENSE
+
 pragma circom 2.0.0;
 
 include "./utils.circom";
diff --git a/circuits/utils.circom b/circuits/utils.circom
index a52979a..e574260 100644
--- a/circuits/utils.circom
+++ b/circuits/utils.circom
@@ -1,3 +1,6 @@
+// Keccak256 hash function (ethereum version).
+// For LICENSE check https://github.com/vocdoni/keccak256-circom/blob/master/LICENSE
+
 pragma circom 2.0.0;
 
 include "../node_modules/circomlib/circuits/gates.circom";
diff --git a/test/circuits/keccak_256_256_test.circom b/test/circuits/keccak_256_256_test.circom
new file mode 100644
index 0000000..1625fd5
--- /dev/null
+++ b/test/circuits/keccak_256_256_test.circom
@@ -0,0 +1,5 @@
+pragma circom 2.0.0;
+
+include "../../circuits/keccak.circom";
+
+component main = Keccak(32*8, 32*8);
diff --git a/test/circuits/keccak256_test.circom b/test/circuits/keccak_32_256_test.circom
similarity index 63%
rename from test/circuits/keccak256_test.circom
rename to test/circuits/keccak_32_256_test.circom
index 789e566..5ded385 100644
--- a/test/circuits/keccak256_test.circom
+++ b/test/circuits/keccak_32_256_test.circom
@@ -2,4 +2,4 @@ pragma circom 2.0.0;
 
 include "../../circuits/keccak.circom";
 
-component main = Keccak(32*8);
+component main = Keccak(4*8, 32*8);
diff --git a/test/keccak.js b/test/keccak.js
index 61feaf0..08211ee 100644
--- a/test/keccak.js
+++ b/test/keccak.js
@@ -8,12 +8,12 @@ const c_tester = require("circom_tester").c;
 const utils = require("./utils");
 const keccak256 = require("keccak256");
 
-describe("Keccak full hash test", function () {
+describe("Keccak 32bytes full hash test", function () {
     this.timeout(100000);
 
     let cir;
     before(async () => {
-	cir = await c_tester(path.join(__dirname, "circuits", "keccak256_test.circom"));
+	cir = await c_tester(path.join(__dirname, "circuits", "keccak_256_256_test.circom"));
 	await cir.loadConstraints();
 	console.log("n_constraints", cir.constraints.length);
     });
@@ -109,3 +109,50 @@ describe("Keccak full hash test", function () {
 	});
     });
 });
+
+describe("Keccak input: 4bytes, output: 32bytes, full hash test", function () {
+    this.timeout(100000);
+
+    let cir;
+    before(async () => {
+	cir = await c_tester(path.join(__dirname, "circuits", "keccak_32_256_test.circom"));
+	await cir.loadConstraints();
+	console.log("n_constraints", cir.constraints.length);
+    });
+
+    it ("Keccak inputSize==32bits: 1 (testvector generated from go)", async () => {
+	const input = [116, 101, 115, 116];
+	const expectedOut = [156, 34, 255, 95, 33, 240, 184, 27, 17, 62, 99,
+	    247, 219, 109, 169, 79, 237, 239, 17, 178, 17, 155, 64, 136, 184,
+	    150, 100, 251, 154, 60, 182, 88];
+
+	const inIn = utils.bytesToBits(input);
+
+	const witness = await cir.calculateWitness({ "in": inIn }, true);
+
+	const stateOut = witness.slice(1, 1+(32*8));
+	const stateOutBytes = utils.bitsToBytes(stateOut);
+	// console.log(stateOutBytes, expectedOut);
+	assert.deepEqual(stateOutBytes, expectedOut);
+    });
+
+    it ("Keccak256 inputSize==32bits, circom-js 1", async () => {
+	let input, inputBits, expectedOut, witness, stateOut, stateOutBytes;
+	input = Buffer.from("test");
+	for(let i=0; i<10; i++) {
+	    inputBits = utils.bytesToBits(input);
+
+	    let jsOutRaw = keccak256(input);
+	    expectedOut = utils.bufferToBytes(jsOutRaw);
+	    console.log(i, "in:", input.toString('hex'), "\n out:", jsOutRaw.toString('hex'));
+
+	    witness = await cir.calculateWitness({ "in": inputBits }, true);
+	    stateOut = witness.slice(1, 1+(32*8));
+	    stateOutBytes = utils.bitsToBytes(stateOut);
+	    assert.deepEqual(stateOutBytes, expectedOut);
+
+	    // assign output[0:4] into input for next iteration
+	    input = jsOutRaw.slice(0, 4);
+	}
+    });
+});