Tested on Safari/Ios/Chrome/Firefox)

Digital_Signature_using _Web_Crypto.js

//Jsfiddle https://jsfiddle.net/h2u4fowj/58/

function str2ab(str) {
  var buf = new ArrayBuffer(str.length);
  var bufView = new Uint8Array(buf);
  for (var i = 0, strLen = str.length; i < strLen; i++) {
    bufView[i] = str.charCodeAt(i);
  }
  return buf;
}
//Create base64 from arraybuffer
function _arrayBufferToBase64(buffer) {
  var binary = '';
  var bytes = new Uint8Array(buffer);
  var len = bytes.byteLength;
  for (var i = 0; i < len; i++) {
    binary += String.fromCharCode(bytes[i]);
  }
  return window.btoa(binary);
}

//Convert base64 to unitArray
function _base64ToArrayBuffer(base64) {
  var binary_string = window.atob(base64);
  var len = binary_string.length;
  var bytes = new Uint8Array(len);
  for (var i = 0; i < len; i++) {
    bytes[i] = binary_string.charCodeAt(i);
  }
  return bytes;
}

var keys = {
  "_id": "58b5acc26886780d006e8353",
  "private_key": {
    "kty": "RSA",
    "n": "ltN-rIU4V88KLRflYWfI94oDDWxOG6x38kXDYjnHRc0U3uyYmb0zPv7hvTF-oG7v947Ckk1uK3Pj26dNy9KxA8LumtRP2sYRKUGR_9vBPCTd3QKe_f7ILg7qw0CYSHBLhnKncKY1e0kWXjLCPbrKXJvGTyVmmt480OsZtl5nc-s",
    "e": "AQAB",
    "d": "hiQdwnRNkxMJeueI06PJghcV9edAZK50k13mksLOb08hY87LPdie7kUkIe8WLrvb4rHubM4-0Jimq-HVeBSv50n3fRkKGowH15oFzDpzRYq0orLiu786WARjpko1vOx6sEioCNIugdCs4OFTSEB8XmbEjuw0c-LESW7C84Ri9Qk",
    "p": "xtbHolLT2lQNCXWlD1PmdU2D9fJsint83ngw1WMWJxxkEa7aLRQnnc3Qp55lzdwkNqSspkyJFuYfswmr6g0MZQ",
    "q": "wi9KnhE7ecR20tY-PYL7s40S8O-z0oSEv0Y_qgk9d5RDNBrRQWt7fbeWDM97jX9EwPKUX2cWlSZaNSqmrtgyDw",
    "dp": "rmNUtzK5hzRMMs2xNB47cwnHAH_bXiErxNnYym2a0jZ-NVwLEZopnKcTps6vLrsyL5KBsWBSo3i0uIt08VL8WQ",
    "dq": "CjCPGtJOq6oajh-97l5kNNzPRKNfbUmU6bCXAKYxeofmKuLJXkR0m3k5v3xXwGoQQou4K3VuYu87RpTxYDVqEw",
    "qi": "B9gwww80iD3I2XQucKW7-xHmagnQAGyYO6xHma-iNSiKLyruBhkuM7fLRMQfcMoeTwxd28NG31ju0xQXZxETWQ"
  },
  "public_key": {
    "kty": "RSA",
    "n": "ltN-rIU4V88KLRflYWfI94oDDWxOG6x38kXDYjnHRc0U3uyYmb0zPv7hvTF-oG7v947Ckk1uK3Pj26dNy9KxA8LumtRP2sYRKUGR_9vBPCTd3QKe_f7ILg7qw0CYSHBLhnKncKY1e0kWXjLCPbrKXJvGTyVmmt480OsZtl5nc-s",
    "e": "AQAB"
  }
}


var private_key = keys.private_key;
var public_key = keys.public_key;
// Fix Apple prefix if needed
if (window.crypto && !window.crypto.subtle && window.crypto.webkitSubtle) {
  window.crypto.subtle = window.crypto.webkitSubtle; // Won't work if subtle already exists
  //Update private key
  console.log("safari browser")
  private_key = str2ab(JSON.stringify(private_key));
  public_key = str2ab(JSON.stringify(public_key));
}
//global variable
var signature_hash;

//****************Sign*********************//
var imported_private_key = '';
window.crypto.subtle.importKey(
    "jwk", //can be "jwk" (public or private), "spki" (public only), or "pkcs8" (private only)
    private_key, { //these are the algorithm options
      name: "RSASSA-PKCS1-v1_5",
      hash: {
        name: "SHA-256"
      }, //can be "SHA-1", "SHA-256", "SHA-384", or "SHA-512"
    },
    false, //whether the key is extractable (i.e. can be used in exportKey)
    ["sign"] //"verify" for public key import, "sign" for private key imports
  )
  .then(function(private_key) {
    console.log("private_key", private_key);
    imported_private_key = private_key;
  })
  .catch(function(err) {
    console.log("Something went wrong while importing the key: " + err.message + "\n" + err.stack);
    //Record Error
  });


var plaintext_buffer = str2ab("pooranprakash");
setTimeout(function() {
  window.crypto.subtle.sign({
        "name": "RSASSA-PKCS1-v1_5",
        "modulusLength": 1024,
        "hash": {
          "name": "SHA-256"
        }
      },
      imported_private_key, //from generateKey or importKey above
      plaintext_buffer //ArrayBuffer of data you want to sign
    ).then(function(signature) {
      console.log("signature", signature);
      //Save  hash
      signature_hash = _arrayBufferToBase64(signature)

    })
    .catch(function(err) {
      console.log("Something went wrong while signing the signature: " + err.message + "\n" + err.stack);
      //Record Error
    })
}, 5000);

//**************************Verify****************************//
window.crypto.subtle.importKey(
    "jwk", //can be "jwk" (public or private), "spki" (public only), or "pkcs8" (private only)
    public_key, { //these are the algorithm options
      name: "RSASSA-PKCS1-v1_5",
      hash: {
        name: "SHA-256"
      }, //can be "SHA-1", "SHA-256", "SHA-384", or "SHA-512"
    },
    false, //whether the key is extractable (i.e. can be used in exportKey)
    ["verify"] //"verify" for public key import, "sign" for private key imports
  )
  .then(function(public_key) {
    //verify file
    imported_public_key = public_key;
  })
  .catch(function(err) {
    console.error(err);
  });

setTimeout(function() {
  window.crypto.subtle.verify({
        "name": "RSASSA-PKCS1-v1_5",
        "modulusLength": 1024,
        "hash": {
          "name": "SHA-256"
        }
      },
      imported_public_key,
      _base64ToArrayBuffer(signature_hash),
      plaintext_buffer
    ).then(function(successful) {
      // Returns either a Blob containing the original plaintext (if verification was successful) or null (if not).
      if (successful) {
        console.log("Signature is valid.");
        return successful
      } else {
        console.log("Signature is invalid.");
        return null;
      }
    })
    .catch(function(err) {
      console.error("Something went wrong verifying: " + err.message + "\n" + err.stack);
    });
}, 10000);