package net.i2p.crypto.eddsa;
/**
* Basic utilities for eddsa.
* Not for external use, not maintained as a public API.
*
* @since 0.9.15
* @author str4d
*
*/
public class Utils {
/**
* Constant-time byte comparison.
* @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.
* @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();
}
}