Port of the RSA algo to javascript and vb-script. Used to for low-level encryption on non-https site.

rsa-encrypt-decrypt-roundtrip-test.asp

<%
REM: An excerpt from RSA Security site FAW "Is RSA patented?"
REM: http://www.rsasecurity.com/rsalabs/faq/6-3-1.html
REM: The patent for the RSA algorithm (U.S. Patent 4,405,829) was issued on September 20, 1983,
REM: exclusively licensed to RSA Security Inc. by the Massachusetts Institute of Technology,
REM: with an expiration date of September 20, 2000. RSA Security maintained a standard,
REM: royalty-based licensing policy that could be modified for special circumstances.
REM: In the U.S., a license has been needed to ëëmake, use or sellíí products that included
REM: the RSA algorithm. However, RSA Security has long allowed free non-commercial use of
REM: the RSA algorithm, with written permission, for academic or university research purposes.
REM:
REM: On September 6, 2000, RSA Security made the RSA algorithm publicly available and waived
REM: its rights to enforce the RSA patent for any development activities that include the
REM: algorithm occurring after September 6, 2000. From this date forward, companies are able
REM: to develop products that incorporate their own implementation of the RSA algorithm and
REM: sell these products in the U.S.
%>

<script>

function dostuff() {
   form.jsencrypted.value = encrypt(form.message.value,form.public.value,form.modulus.value);
   form.jsdecrypted.value = decrypt(form.jsencrypted.value,form.private.value,form.modulus.value);
   return
}

function encrypt(txt, key, mkey) {
   //return Math.pow(num,key) % mkey

   if (txt.length == 0) return
   encrypt = ""
	for (i = 0; i < txt.length; i++) {
      char = txt.substr(i,1);                               //get single characters
      dec = char.toString().charCodeAt(0);                  //convert each character to ASCII decimal
      cipher = crypt(dec, key, mkey)                        //encrypt ASCII decimals
	   encrypt = encrypt.concat(padNum(jsToHex(cipher, 4)))  //convert decimals to hex (4 character blocks)
   }
   return encrypt;
}

function decrypt(hex, key, mkey) {
   decrypt = ""
	for (i = 0; i < hex.length; i=i+4) {
      block = hex.substr(i,4);                              //get hex block
      cipher = jsToDec(block);                              //convert each hex block to cipher
      dec = crypt(cipher, key, mkey)                        //decrypt the cipher back to ASCII decimal
	   decrypt = decrypt.concat(String.fromCharCode(dec))    //convert decimals to hex (4 character blocks)
   }
   return decrypt;
}



function crypt (num, key, mkey) {
   y = (num*num) % mkey

   if ( key % 2 == 0) {
      x = 1
   } else {
      x = num
   }
   for ( var i = 1; i <= key/2; i++) {
      x = (x * y) % mkey
   }
   return x
}

function jsToHex(dec) {
   dec=dec*1;
   return padNum(dec.toString(16),4);
}

function jsToDec(hex) {
   preHex = "0x"
   return Math.floor(preHex.concat(hex));
}

function padNum(str,len) {
   pad = "0"
   while(str.length < 4) {
      str = pad.concat(str);
   }
   return str.toUpperCase()
}

</script>


<%
	Function NumberToHex(ByRef pLngNumber, ByRef pLngLength)
		NumberToHex = Right(String(pLngLength, "0") & Hex(pLngNumber), pLngLength)
	End Function

	Function HexToNumber(ByRef pStrHex)
		HexToNumber = CLng("&h" & pStrHex)
	End Function

p1   = request.form("prime1")
p2   = request.form("prime2")
pubKey    = request.form("public")
priKey    = request.form("private")
modKey    = request.form("modulus")

origText = request.form("message")
coded = encrypt(origText,pubKey,modKey)
convText = decrypt(coded,priKey,modKey)


   Function Encrypt(txt, key, mkey)
      REM: solve for RSA encryption formula
      REM: Cipher = Txt^key % modulus

      If Len(txt) = 0 Then Exit Function
		For i = 1 To Len(txt)
			dec = Asc(Mid(txt, i, 1))                  REM: convert each character to ASCII decimal
			cipher = Crypt(dec, key, mkey)             REM: encrypt ASCII decimals
		   Encrypt = Encrypt & NumberToHex(cipher, 4) REM: convert decimals to hex (4 character blocks)
		Next
	End Function

   Function Decrypt(hex, key, mkey)
      REM: Solve for RSA decryption formula
      REM: Txt = Cipher^key % modulus

		Decode = ""
		For i = 1 To Len(hex) Step 4
			cipher = HexToNumber(Mid(hex, i, 4))   REM: convert the hex back to cipher
			dec = Crypt(cipher, key, mkey)         REM: decrypt cipher
		   Decrypt = Decrypt & Chr(dec)           REM: convert ASCII decimal back to character, build result
		Next
	End Function

	Function Crypt(num, key, mkey)
      REM: Modular exponentiation and Fermat/Eular  theorem x^p-1 = 1%P
      REM: If I really knew what that meant I'd be making more money :-)

      y = (num * num) Mod mkey

      If key Mod 2 = 0 Then
   		x = 1
   	Else
   		x = num
   	End If

   	For i = 1 To key / 2
   	   x = (x * y) Mod mkey
   	Next
      Crypt = x
   End Function



%>


<form method="post" name=form>
   <table>
      <tr><td>prime 1:   </td><td>p1: </td><td><input type=text name=prime1 value=11>      </td></tr>
      <tr><td>prime 2:   </td><td>p2: </td><td><input type=text name=prime1 value=211>     </td></tr>
      <tr><td>modulus:   </td><td> N: </td><td><input type=text name=modulus value=2321>   </td></tr>
      <tr><td>public:    </td><td> E: </td><td><input type=text name=public value=11>      </td></tr>
      <tr><td>private:   </td><td> D: </td><td><input type=text name=private value=191>    </td></tr>


      <tr><td>message:   </td><td> T: </td><td><input type=text name=message value="<%=origText%>">   </td></tr>
      <tr><td>encrypted: </td><td> C: </td><td><input type=text name=encrypted value="<%=coded%>"> </td><td><input type=text name=jsencrypted value=""> </td></tr>
      <tr><td>decrypted: </td><td> T: </td><td><input type=text name=decrypted value="<%=convText%>"> </td><td><input type=text name=jsdecrypted value=""> </td></tr>

      <tr><td colspan=2><input type=submit></td><td><button onclick="dostuff();">dostuff</button></td></tr>

   </table>
</form>  

rsa-encrypt-decrypt.js

// Better alternatives
// http://www.ohdave.com/rsa/
// http://www.hanewin.net/encrypt/rsa/rsa.htm
// http://www.cs.pitt.edu/~kirk/cs1501/notes/rsademo/
// https://ziyan.info/2008/10/javascript-rsa/

//====================================================
// An excerpt from RSA Security site FAW "Is RSA patented?"
// http://www.rsasecurity.com/rsalabs/faq/6-3-1.html
// The patent for the RSA algorithm (U.S. Patent 4,405,829) was issued on September 20, 1983,
// exclusively licensed to RSA Security Inc. by the Massachusetts Institute of Technology,
// with an expiration date of September 20, 2000. RSA Security maintained a standard,
// royalty-based licensing policy that could be modified for special circumstances.
// In the U.S., a license has been needed to ‘‘make, use or sell’’ products that included
// the RSA algorithm. However, RSA Security has long allowed free non-commercial use of
// the RSA algorithm, with written permission, for academic or university research purposes.
//
// On September 6, 2000, RSA Security made the RSA algorithm publicly available and waived
// its rights to enforce the RSA patent for any development activities that include the
// algorithm occurring after September 6, 2000. From this date forward, companies are able
// to develop products that incorporate their own implementation of the RSA algorithm and
// sell these products in the U.S.
//
// ModulusKey = 2321
// PublicKey = 11
// Private Key = 191 

//The following is an example of how to call the encryption function:
// <script for="form" event="onsubmit">
//    form.js_asp.value = encrypt(form.password.value,11,2321);
//    form.submit();
// </script>
//
// <script for="window" event="onload">
//    form.asp_js.value = decrypt(form.asp_js.value,11,2321);
// </script>


function encrypt(txt, key, mkey) {
   //return Math.pow(num,key) % mkey

   if (txt.length == 0) return
   strEncrypt = ""
	for (i = 0; i < txt.length; i++) {
      char = txt.substr(i,1);                               //get single characters
      dec = char.toString().charCodeAt(0);                  //convert each character to ASCII decimal
      cipher = crypt(dec, key, mkey)                        //encrypt ASCII decimals
	   strEncrypt = strEncrypt.concat(padNum(jsToHex(cipher, 4)))  //convert decimals to hex (4 character blocks)
   }
   return strEncrypt;
}

function decrypt(hex, key, mkey) {
   decrypt = ""
	for (i = 0; i < hex.length; i=i+4) {
      block = hex.substr(i,4);                              //get hex block
      cipher = jsToDec(block);                              //convert each hex block to cipher
      dec = crypt(cipher, key, mkey)                        //decrypt the cipher back to ASCII decimal
	   decrypt = decrypt.concat(String.fromCharCode(dec))    //convert decimals to hex (4 character blocks)
   }
   return decrypt;
}

function crypt (num, key, mkey) {
   y = (num*num) % mkey

   if ( key % 2 == 0) {
      x = 1
   } else {
      x = num
   }
   for ( var i = 1; i <= key/2; i++) {
      x = (x * y) % mkey
   }
   return x
}

function jsToHex(dec) {
   dec=dec*1;
   return padNum(dec.toString(16),4);
}

function jsToDec(hex) {
   preHex = "0x"
   return Math.floor(preHex.concat(hex));
}

function padNum(str,len) {
   pad = "0"
   while(str.length < 4) {
      str = pad.concat(str);
   }
   return str.toUpperCase()
}

rsa-vbs-encrypt-decrypt.vbs

REM: An excerpt from RSA Security site FAW "Is RSA patented?"
REM: http://www.rsasecurity.com/rsalabs/faq/6-3-1.html
REM: The patent for the RSA algorithm (U.S. Patent 4,405,829) was issued on September 20, 1983,
REM: exclusively licensed to RSA Security Inc. by the Massachusetts Institute of Technology,
REM: with an expiration date of September 20, 2000. RSA Security maintained a standard,
REM: royalty-based licensing policy that could be modified for special circumstances.
REM: In the U.S., a license has been needed to ëëmake, use or sellíí products that included
REM: the RSA algorithm. However, RSA Security has long allowed free non-commercial use of
REM: the RSA algorithm, with written permission, for academic or university research purposes.
REM:
REM: On September 6, 2000, RSA Security made the RSA algorithm publicly available and waived
REM: its rights to enforce the RSA patent for any development activities that include the
REM: algorithm occurring after September 6, 2000. From this date forward, companies are able
REM: to develop products that incorporate their own implementation of the RSA algorithm and
REM: sell these products in the U.S.

REM: The following is based on:
REM: Prime 1 = 11
REM: Prime 2 = 211
REM: ModulusKey = 2321
REM: PublicKey = 11
REM: PrivateKey = 191 This should not be used on the external javascript

   Function Encrypt(txt, key, mkey)
      REM: solve for RSA encryption formula
      REM: Cipher = Txt^key % modulus

      If Len(txt) = 0 Then Exit Function
		On Error Resume Next
		For i = 1 To Len(txt)
			dec = Asc(Mid(txt, i, 1))                  REM: convert each character to ASCII decimal
			cipher = Crypt(dec, key, mkey)             REM: encrypt ASCII decimals
		   Encrypt = Encrypt & NumberToHex(cipher, 4) REM: convert decimals to hex (4 character blocks)
		Next
		If Err Then
		   Session.Abandon()
		End If
		On Error GoTo 0
	End Function

   Function Decrypt(hex, key, mkey)
      REM: Solve for RSA decryption formula
      REM: Txt = Cipher^key % modulus

      REM: If hex is NULL then "For i = 1 To Len(hex)" throws an error
      If Len(hex) = 0 OR isNull(hex) Then Exit Function

		Decode = ""
		For i = 1 To Len(hex) Step 4
			cipher = HexToNumber(Mid(hex, i, 4))   REM: convert the hex back to cipher
			dec = Crypt(cipher, key, mkey)         REM: decrypt cipher
		   On Error Resume Next
		   Decrypt = Decrypt & Chr(dec)           REM: convert ASCII decimal back to character, build result
		   If Err Then
		      Session.Abandon()
		   End If
		   On Error GoTo 0
		Next
	End Function

	Function Crypt(num, key, mkey)
      REM: Modular exponentiation and Fermat/Eular  theorem x^p-1 = 1%P
      REM: If I really knew what that meant I'd be making more money :-)
      On Error Resume Next
      y = (num * num) Mod mkey

      If key Mod 2 = 0 Then
   		x = 1
   	Else
   		x = num
   	End If

   	For i = 1 To key / 2
   	   x = (x * y) Mod mkey
   	Next
   	If (Err) Then
   	   Session.Abandon()
   	End If
   	On Error GoTo 0
      Crypt = x
   End Function

   Function NumberToHex(ByRef pLngNumber, ByRef pLngLength)
		'NumberToHex = Right(String(pLngLength, "0") & Hex(pLngNumber), pLngLength)

		On Error Resume Next
	   NumberToHex = Right(String(pLngLength, "0") & Hex(pLngNumber), pLngLength)
	   If Err Then
	      Session.Abandon()
	   End If
	   On Error GoTo 0

	End Function

	Function HexToNumber(ByRef pStrHex)
		'HexToNumber = CLng("&h" & pStrHex)

		On Error Resume Next
	   HexToNumber = CLng("&h" & pStrHex)
	   If Err Then
	      Session.Abandon()
	   End If
	   On Error GoTo 0
	End Function

	Function jsEscapeQuote(string)
      Return Replace(string,"'","\'")
   End Function

Wrote this a loooong time ago (circa 2001?). Thought people might find it useful. There are several better alternatives, t least, I assume they know more about encryption than I do.

http://www.ohdave.com/rsa/

http://www.hanewin.net/encrypt/rsa/rsa.htm

http://www.cs.pitt.edu/~kirk/cs1501/notes/rsademo/

https://ziyan.info/2008/10/javascript-rsa/