RSA encryption with public key in salesforce apex

RsaEncryption.cls

public with sharing class RsaEncryption {

    private String modulus;
    private String exponent;

    // Hex digits
    private static final String DIGITS = '0123456789abcdef';
    private static final Decimal HEX_BASE = 16;

    public RsaEncryption(String modulus, String exponent) {
        this.modulus = modulus;
        this.exponent = exponent;
    }

    public String encrypt(String input) {
        Blob mod = EncodingUtil.base64Decode(modulus);
        Blob exp = EncodingUtil.base64Decode(exponent);

        // Pad password.nonce
        Blob pn = Blob.valueOf(String.fromCharArray(pkcs1Pad2(input, mod.size() - 1)));

        Decimal modDec = hexToDecimal(EncodingUtil.convertToHex(mod));
        Decimal expDec = hexToDecimal(EncodingUtil.convertToHex(exp));
        Decimal pnDec = hexToDecimal(EncodingUtil.convertToHex(pn));

        // Calcluate padded^exp % mod and convert to hex
        Decimal result = modPow(pnDec, expDec, modDec);
        String hexResult = decimalToHex(result);
        // If length is uneven, add an extra 0
        if ((hexResult.length() & 1) == 1) {
            hexResult = '0' + hexResult;
        }

        // Generate the data to be encrypted.
        Blob encodedData = EncodingUtil.convertFromHex(hexResult);
        return EncodingUtil.base64Encode(encodedData);
    }

    @testVisible
    private static Decimal hexToDecimal(String hex) {
        Decimal result = 0;
        integer length = hex.length();
        integer i = 0;
        while(i < length) {
            integer hexByte = DIGITS.indexOf(hex.substring(i, i + 1).toLowerCase());
            i++;
            result += hexByte * HEX_BASE.pow(length - i);
        }
        return result;
    }

    @testVisible
    private static String decimalToHex(Decimal d) {
        String hex = '';
        while (d > 0) {
            Decimal digit = modulus(d, HEX_BASE); // rightmost digit
            hex = DIGITS.substring(digit.intValue(), digit.intValue() + 1) + hex; // string concatenation
            d = d.divide(16, 0, RoundingMode.FLOOR);
        }
        return hex;
    }

    // base^exp % mod
    @testVisible
    private static Decimal modPow(Decimal base, Decimal exp, Decimal mod) {
        if (base < 1 || exp < 0 || mod < 1) {
            return -1;
        }

        Decimal result = 1;
        while (exp > 0) {
           if ((exp.longValue() & 1) == 1) {
               result = modulus((result * base), mod);
           }
           base = modulus((base * base), mod);
           exp = exp.divide(2, 0, RoundingMode.FLOOR);
        }
        return result;
    }

    // dividend % divisor
    @testVisible
    private static Decimal modulus(Decimal dividend, Decimal divisor) {
        Decimal d = dividend.divide(divisor, 0, RoundingMode.FLOOR);
        return dividend - (d * divisor);
    }

    // Pad using PKCS#1 v.2. See https://en.wikipedia.org/wiki/PKCS_1
    // s = String to pad
    // n = bytes to fill must be bigger than s.length()
    @testVisible
    private static List<integer> pkcs1Pad2(String s, integer n) {
        // Byte array
        List<integer> ba = new List<integer>();
        // Fill array with zeros to get the right size
        for(integer i = 0; i < n; i++) {
            ba.add(0);
        }
        integer i = s.length() - 1;
        while(i >= 0 && n > 0) {
            ba.set(--n, s.charAt(i--));
        }
        ba.set(--n, 0);
        while(n > 2) { // random non-zero pad
            // Since the array is converted to a string, choose integers that corresponds
            // to a proper char code see http://www.asciitable.com
            integer rnd = Math.round(Math.random() * (127 - 32) + 32);
            ba.set(--n, rnd);
        }
        ba.set(--n, 2);
        ba.set(--n, 0);
        return ba;
    }

}

Not so simple to understand how to use this code. You need to have 2 parameters : modulus and exponent.
Do you have a example explaining the format for these parameters ?

I took the gist(s) like that one I implemented RSA OAEP SHA-256 based on it. It has few shell scripts to generate keys and prepare them to be used with Apex. It has a test class with example of how to be used. Hope it will be helpful for the community. One thing to remember is that it takes a lot of CPU for 4K RSA OAEP SHA256 decryption.

https://github.com/alex-shekhter/apex-crypto-rsa-oaep-sha256

If I have an RSA public key, how do I get the modulus and exponent? Has anyone successfully implemented RSA public key encryption with this code?

openssl rsa -pubin -inform PEM -text -noout < YOUR_PUBLIC_KEY_IN_PEM_FORMAT

can i get them in apex code ?

Yes you can. Take a look at the https://github.com/mattandneil/apex-rsa-sha-512/blob/master/CryptoRsaSha512.cls Inner class Asn will allow you to obtain modulus and public exponent from the PEM file. Good luck

…

On Tue, Aug 8, 2023 at 10:19 PM rickywgr ***@***.***> wrote: ***@***.**** commented on this gist. ------------------------------ can i get them in apex code ? — Reply to this email directly, view it on GitHub <https://gist.github.com/karmats/4270441be5a34fff7062#gistcomment-4655649> or unsubscribe <https://github.com/notifications/unsubscribe-auth/AB4RMCCXTFFMKRIFX7D6O2LXULXSHBFKMF2HI4TJMJ2XIZLTSKBKK5TBNR2WLJDHNFZXJJDOMFWWLK3UNBZGKYLEL52HS4DFQKSXMYLMOVS2I5DSOVS2I3TBNVS3W5DIOJSWCZC7OBQXE5DJMNUXAYLOORPWCY3UNF3GS5DZVRZXKYTKMVRXIX3UPFYGLK2HNFZXIQ3PNVWWK3TUUZ2G64DJMNZZDAVEOR4XAZNEM5UXG5FFOZQWY5LFVAZTCNZRG43DSOFHORZGSZ3HMVZKMY3SMVQXIZI> . You are receiving this email because you commented on the thread. Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub> .

Thanks, I'll spend some time looking into it ! At 2023-08-09 16:12:23, "alex-shekhter" ***@***.***> wrote: @alex-shekhter commented on this gist. Yes you can. Take a look at the https://github.com/mattandneil/apex-rsa-sha-512/blob/master/CryptoRsaSha512.cls Inner class Asn will allow you to obtain modulus and public exponent from the PEM file. Good luck

On Tue, Aug 8, 2023 at 10:19 PM rickywgr ***@***.***> wrote: ***@***.**** commented on this gist. ------------------------------ can i get them in apex code ? — Reply to this email directly, view it on GitHub <https://gist.github.com/karmats/4270441be5a34fff7062#gistcomment-4655649> or unsubscribe <https://github.com/notifications/unsubscribe-auth/AB4RMCCXTFFMKRIFX7D6O2LXULXSHBFKMF2HI4TJMJ2XIZLTSKBKK5TBNR2WLJDHNFZXJJDOMFWWLK3UNBZGKYLEL52HS4DFQKSXMYLMOVS2I5DSOVS2I3TBNVS3W5DIOJSWCZC7OBQXE5DJMNUXAYLOORPWCY3UNF3GS5DZVRZXKYTKMVRXIX3UPFYGLK2HNFZXIQ3PNVWWK3TUUZ2G64DJMNZZDAVEOR4XAZNEM5UXG5FFOZQWY5LFVAZTCNZRG43DSOFHORZGSZ3HMVZKMY3SMVQXIZI> . You are receiving this email because you commented on the thread. Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub> .

— Reply to this email directly, view it on GitHub or unsubscribe. You are receiving this email because you commented on the thread. Triage notifications on the go with GitHub Mobile for iOS or Android.