diff --git a/src/crypto/crypto.js b/src/crypto/crypto.js
index 47873961..53085d08 100644
--- a/src/crypto/crypto.js
+++ b/src/crypto/crypto.js
@@ -18,6 +18,7 @@
 // The GPG4Browsers crypto interface
 
 /**
+ * @requires bn.js
  * @requires asmcrypto.js
  * @requires crypto/public_key
  * @requires crypto/cipher
@@ -30,8 +31,8 @@
  * @module crypto/crypto
  */
 
+import BN from 'bn.js';
 import { RSA_RAW, BigNumber, Modulus } from 'asmcrypto.js';
-import BigInteger from './public_key/jsbn';
 import publicKey from './public_key';
 import cipher from './cipher';
 import random from './random';
@@ -67,12 +68,10 @@ export default {
       switch (algo) {
         case 'rsa_encrypt':
         case 'rsa_encrypt_sign': {
-          const n = util.str2Uint8Array(publicParams[0].toBytes());
-          const e = util.str2Uint8Array(publicParams[1].toBytes());
-          m = data.write().slice(2); // FIXME
-          return constructParams(types, [
-            new BigInteger(util.hexidump(RSA_RAW.encrypt(m, [n, e])), 16) // FIXME
-          ]);
+          const n = publicParams[0].toUint8Array();
+          const e = publicParams[1].toUint8Array();
+          m = data.toUint8Array();
+          return constructParams(types, [new BN(RSA_RAW.encrypt(m, [n, e]))]);
         }
         case 'elgamal': {
           const elgamal = new publicKey.elgamal();
@@ -114,13 +113,13 @@ export default {
       switch (algo) {
         case 'rsa_encrypt_sign':
         case 'rsa_encrypt': {
-          const c = util.str2Uint8Array(dataIntegers[0].toBytes());
-          const n = util.str2Uint8Array(keyIntegers[0].toBytes()); // pq
-          const e = util.str2Uint8Array(keyIntegers[1].toBytes());
-          const d = util.str2Uint8Array(keyIntegers[2].toBytes()); // de = 1 mod (p-1)(q-1)
-          const p = util.str2Uint8Array(keyIntegers[3].toBytes());
-          const q = util.str2Uint8Array(keyIntegers[4].toBytes());
-          const u = util.str2Uint8Array(keyIntegers[5].toBytes()); // q^-1 mod p
+          const c = dataIntegers[0].toUint8Array();
+          const n = keyIntegers[0].toUint8Array(); // pq
+          const e = keyIntegers[1].toUint8Array();
+          const d = keyIntegers[2].toUint8Array(); // de = 1 mod (p-1)(q-1)
+          const p = keyIntegers[3].toUint8Array();
+          const q = keyIntegers[4].toUint8Array();
+          const u = keyIntegers[5].toUint8Array(); // q^-1 mod p
           const dd = BigNumber.fromArrayBuffer(d);
           const dp = new Modulus(
             BigNumber.fromArrayBuffer(p).subtract(BigNumber.ONE)
@@ -128,9 +127,7 @@ export default {
           const dq = new Modulus(
             BigNumber.fromArrayBuffer(q).subtract(BigNumber.ONE)
           ).reduce(dd).toBytes(); // d mod (q-1)
-          return new BigInteger(
-            util.hexidump(RSA_RAW.decrypt(c, [n, e, d, q, p, dq, dp, u]).slice(1)), 16 // FIXME
-          );
+          return new BN(RSA_RAW.decrypt(c, [n, e, d, q, p, dq, dp, u]).slice(1)); // FIXME remove slice
         }
         case 'elgamal': {
           const elgamal = new publicKey.elgamal();
diff --git a/src/crypto/signature.js b/src/crypto/signature.js
index 0bbbbbd6..4136802c 100644
--- a/src/crypto/signature.js
+++ b/src/crypto/signature.js
@@ -38,10 +38,10 @@ export default {
         // RSA Encrypt-Only [HAC]
       case 3: {
         // RSA Sign-Only [HAC]
-        const n = util.str2Uint8Array(publickey_MPIs[0].toBytes());
+        const n = publickey_MPIs[0].toUint8Array();
         const k = publickey_MPIs[0].byteLength();
-        const e = util.str2Uint8Array(publickey_MPIs[1].toBytes());
-        m = msg_MPIs[0].write().slice(2); // FIXME
+        const e = publickey_MPIs[1].toUint8Array();
+        m = msg_MPIs[0].toUint8Array();
         const EM = RSA_RAW.verify(m, [n, e]);
         const EM2 = pkcs1.emsa.encode(hash_algo, data, k);
         return util.hexidump(EM) === EM2;
@@ -111,13 +111,11 @@ export default {
         // RSA Encrypt-Only [HAC]
       case 3: {
         // RSA Sign-Only [HAC]
-        const n = util.str2Uint8Array(keyIntegers[0].toBytes());
+        const n = keyIntegers[0].toUint8Array();
         const k = keyIntegers[0].byteLength();
-        const e = util.str2Uint8Array(keyIntegers[1].toBytes());
-        d = util.str2Uint8Array(keyIntegers[2].toBytes());
-        m = util.hex2Uint8Array(
-          '00'+pkcs1.emsa.encode(hash_algo, data, k) // FIXME
-        );
+        const e = keyIntegers[1].toUint8Array();
+        d = keyIntegers[2].toUint8Array();
+        m = util.hex2Uint8Array('00'+pkcs1.emsa.encode(hash_algo, data, k)); // FIXME remove '00'
         return util.Uint8Array2MPI(RSA_RAW.sign(m, [n, e, d]));
       }
       case 17: {
diff --git a/src/type/mpi.js b/src/type/mpi.js
index 466f6a5f..496e5a5c 100644
--- a/src/type/mpi.js
+++ b/src/type/mpi.js
@@ -46,6 +46,8 @@ export default function MPI(data) {
   /** An implementation dependent integer */
   if (data instanceof BigInteger) {
     this.fromBigInteger(data);
+  } else if (data instanceof BN) {
+    this.fromBytes(util.Uint8Array2str(data.toArrayLike(Uint8Array)));
   } else if (util.isString(data)) {
     this.fromBytes(data);
   } else {
@@ -92,8 +94,11 @@ MPI.prototype.fromBytes = function (bytes) {
 };
 
 MPI.prototype.toBytes = function () {
-  const bytes = util.Uint8Array2str(this.write());
-  return bytes.substr(2);
+  return util.Uint8Array2str(this.toUint8Array());
+};
+
+MPI.prototype.toUint8Array = function () {
+  return this.write().slice(2);
 };
 
 MPI.prototype.byteLength = function () {