public static String reverseKeyword(String hexEncodedHash, String alphabet, int max) {
        BigInteger numericOfHash = new BigInteger(hexEncodedHash, 16); // radix = [2..36]
        BigInteger divider = BigInteger.valueOf(alphabet.length());
        StringBuilder sb = new StringBuilder(max);
        for(int i = 0; i < max; i++) {
            int mod = numericOfHash.mod(divider).intValue();
            sb.append(alphabet.charAt(mod));
            numericOfHash = numericOfHash.divide(divider);
        }
        return sb.toString();
    }

    @Test
    void testRevPwd1() {
        // dbeead -> ddddbb
        String hash1 = PwdProcessor.hashPwd("dbeead"); // SHA-1
        assertEquals("1347d73da9d496705783af314ce992137503e649a10c3b96026b00c2922440f9", hash1);
        String revPwd1 = PwdProcessor.reverseKeyword("1347d73da9d496705783af314ce992137503e649a10c3b96026b00c2922440f9", "abcdefghjklmnopqrstvwxyz0123456789", 6);
        assertEquals("ky9aew", revPwd1);
    }

reverseKeyword(hashPwd(reverseKeyword(.....))) 

Benchmark                                Mode  Cnt        Score       Error  Units
PwdProcessorBenchmark.testHash          thrpt   10  1549404.249 ± 41868.835  ops/s
PwdProcessorBenchmark.testReverseHash   thrpt   10   229683.377 ±  5370.196  ops/s
PwdProcessorBenchmark.testReverseHash2  thrpt   10   313369.002 ±  6880.737  ops/s

    public static String hashPwd(String pwd) {
        sha256.reset();
        sha256.update(pwd.getBytes(StandardCharsets.UTF_8));
        return Hex.encodeHexString(sha256.digest());
    }

    public static String reversePwd(String hexEncodedHash, String alphabet, int max) {
        BigInteger numericOfHash = new BigInteger(hexEncodedHash, 16); // radix = [2..36]
        BigInteger divider = BigInteger.valueOf(alphabet.length());
        StringBuilder sb = new StringBuilder(max);
        for(int i = 0; i < max; i++) {
            int mod = numericOfHash.mod(divider).intValue();
            sb.append(alphabet.charAt(mod));
            numericOfHash = numericOfHash.divide(divider);
        }
        return sb.toString();
    }

    public static String reversePwd2(String hexEncodedHash, String alphabet, int max) {
        BigInteger numericOfHash = new BigInteger(hexEncodedHash, 16); // radix = [2..36]
        BigInteger divider = BigInteger.valueOf(alphabet.length());
        StringBuilder sb = new StringBuilder(max);
        for(int i = 0; i < max; i++) {
            BigInteger[] res = numericOfHash.divideAndRemainder(divider);
           int mod = res[1].intValue();
            sb.append(alphabet.charAt(mod));
            numericOfHash = res[0];
        }
        return sb.toString();
    }

1347d73da9d496705783af314ce992137503e649a10c3b96026b00c2922440f9

PwdProcessor.reverseKeyword(cropLetters(sha256value, 256, 36)); // 256 bits per hash, and 34 symbols (divider)