EdDSA-Java by str4d

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EdDSA-Java has waived all copyright and related or neighboring rights
to EdDSA-Java.

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work. If not, see <https://creativecommons.org/publicdomain/zero/1.0/>.

package net.i2p.crypto.eddsa;

/**

 Basic utilities for EdDSA.
 Not for external use, not maintained as a public API.

 @author str4d

/

public class Utils {

/**
   Constant-time byte comparison.
   @param b a byte
   @param c a byte
   @return 1 if b and c are equal, 0 otherwise.
  /
public static int equal(int b, int c) {
    int result = 0;
    int xor = b ^ c;
    for (int i = 0; i < 8; i++) {
        result |= xor >> i;
    }
    return (result ^ 0x01) & 0x01;
}

/**
   Constant-time byte[] comparison.
   @param b a byte[]
   @param c a byte[]
   @return 1 if b and c are equal, 0 otherwise.
  /
public static int equal(byte[] b, byte[] c) {
    int result = 0;
    for (int i = 0; i < 32; i++) {
        result |= b[i] ^ c[i];
    }

    return equal(result, 0);
}

/**
   Constant-time determine if byte is negative.
   @param b the byte to check.
   @return 1 if the byte is negative, 0 otherwise.
  /
public static int negative(int b) {
    return (b >> 8) & 1;
}

/**
   Get the i'th bit of a byte array.
   @param h the byte array.
   @param i the bit index.
   @return 0 or 1, the value of the i'th bit in h
  /
public static int bit(byte[] h, int i) {
    return (h[i >> 3] >> (i & 7)) & 1;
}

/**
   Converts a hex string to bytes.
   @param s the hex string to be converted.
   @return the byte[]
  /
public static byte[] hexToBytes(String s) {
    int len = s.length();
    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                + Character.digit(s.charAt(i+1), 16));
    }
    return data;
}

/**
   Converts bytes to a hex string.
   @param raw the byte[] to be converted.
   @return the hex representation as a string.
  /
public static String bytesToHex(byte[] raw) {
    if ( raw == null ) {
        return null;
    }
    final StringBuilder hex = new StringBuilder(2 * raw.length);
    for (final byte b : raw) {
        hex.append(Character.forDigit((b & 0xF0) >> 4, 16))
        .append(Character.forDigit((b & 0x0F), 16));
    }
    return hex.toString();
}

}