M circuits/babyjub.circom → circuits/babyjub.circom

@@ -17,6 +17,9 @@ You should have received a copy of the GNU General Public License
     along with circom. If not, see <https://www.gnu.org/licenses/>.
 */
 
+include "bitify.circom";
+include "escalarmulfix.circom";
+
 template BabyAdd() {
     signal input x1;
     signal input y1;
@@ -77,3 +80,27 @@ y2 <== y*y;
 
     a*x2 + y2 === 1 + d*x2*y2;
 }
+
+// Extracts the public key from private key
+template BabyPbk() {
+    signal private input  in;
+    signal         output Ax;
+    signal         output Ay;
+
+    var BASE8 = [
+        17777552123799933955779906779655732241715742912184938656739573121738514868268,
+        2626589144620713026669568689430873010625803728049924121243784502389097019475
+    ];
+
+    component pvkBits = Num2Bits(253);
+    pvkBits.in <== in;
+
+    component mulFix = EscalarMulFix(253, BASE8);
+
+    var i;
+    for (i=0; i<253; i++) {
+        mulFix.e[i] <== pvkBits.out[i];
+    }
+    Ax  <== mulFix.out[0];
+    Ay  <== mulFix.out[1];
+}

M test/babyjub.js → test/babyjub.js

@@ -3,10 +3,12 @@ const path = require("path");
 const snarkjs = require("snarkjs");
 const compiler = require("circom");
 
-const assert = chai.assert;
+const createBlakeHash = require("blake-hash");
+const eddsa = require("../src/eddsa.js");
 
-const bigInt = require("big-integer");
+const assert = chai.assert;
 
+const bigInt = require("snarkjs").bigInt;
 
 describe("Baby Jub test", function () {
     let circuitAdd;
@@ -22,6 +24,11 @@
         const cirDefTest = await compiler(path.join(__dirname, "circuits", "babycheck_test.circom"));
         circuitTest = new snarkjs.Circuit(cirDefTest);
         console.log("NConstrains BabyTest: " + circuitTest.nConstraints);
+
+        const cirDefPbk = await compiler(path.join(__dirname, "circuits", "babypbk_test.circom"));
+        circuitPbk = new snarkjs.Circuit(cirDefPbk);
+        console.log("NConstrains BabyPbk: " + circuitPbk.nConstraints);
+
     });
 
     it("Should add point (0,1) and (0,1)", async () => {
@@ -95,6 +102,24 @@ assert(false, "Should be a valid point");
         } catch(err) {
             assert.equal(err.message, "Constraint doesn't match: 168700 != 1");
         }
+    });
+
+    it("Should extract the public key from the private one", async () => {    
+
+        const rawpvk = Buffer.from("0001020304050607080900010203040506070809000102030405060708090021", "hex");
+        const pvk    = eddsa.pruneBuffer(createBlakeHash("blake512").update(rawpvk).digest().slice(0,32));
+        const S      = bigInt.leBuff2int(pvk).shr(3);
+
+        const A      = eddsa.prv2pub(rawpvk);
+
+        const input = {
+            in : S,
+            Ax : A[0],
+            Ay : A[1]
+        }
+
+        const w = circuitPbk.calculateWitness(input);
+        assert(circuitPbk.checkWitness(w));
     });
 
 });

A test/circuits/babypbk_test.circom

@@ -0,0 +1,3 @@
+include "../../circuits/babyjub.circom";
+
+component main = BabyPbk();