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/*
* Copyright (C) 2012-2014 Dominik Schürmann <dominik@dominikschuermann.de>
* Copyright (C) 2010-2014 Thialfihar <thi@thialfihar.org>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.sufficientlysecure.keychain.pgp;
import android.content.Context;
import android.graphics.Color;
import android.text.Spannable;
import android.text.SpannableStringBuilder;
import android.text.style.ForegroundColorSpan;
import org.spongycastle.bcpg.PublicKeyAlgorithmTags;
import org.spongycastle.util.encoders.Hex;
import org.sufficientlysecure.keychain.Constants;
import org.sufficientlysecure.keychain.R;
import org.sufficientlysecure.keychain.util.Log;
import java.security.DigestException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Locale;
public class PgpKeyHelper {
public static String getAlgorithmInfo(int algorithm) {
return getAlgorithmInfo(null, algorithm, 0);
}
public static String getAlgorithmInfo(Context context, int algorithm) {
return getAlgorithmInfo(context, algorithm, 0);
}
/**
* Based on <a href="http://tools.ietf.org/html/rfc2440#section-9.1">OpenPGP Message Format</a>
*/
public static String getAlgorithmInfo(Context context, int algorithm, int keySize) {
String algorithmStr;
switch (algorithm) {
case PublicKeyAlgorithmTags.RSA_ENCRYPT:
case PublicKeyAlgorithmTags.RSA_GENERAL:
case PublicKeyAlgorithmTags.RSA_SIGN: {
algorithmStr = "RSA";
break;
}
case PublicKeyAlgorithmTags.DSA: {
algorithmStr = "DSA";
break;
}
case PublicKeyAlgorithmTags.ELGAMAL_ENCRYPT:
case PublicKeyAlgorithmTags.ELGAMAL_GENERAL: {
algorithmStr = "ElGamal";
break;
}
case PublicKeyAlgorithmTags.ECDSA:
case PublicKeyAlgorithmTags.ECDH: {
algorithmStr = "ECC";
break;
}
default: {
if (context != null) {
algorithmStr = context.getResources().getString(R.string.unknown_algorithm);
} else {
algorithmStr = "unknown";
}
break;
}
}
if (keySize > 0)
return algorithmStr + ", " + keySize + " bit";
else
return algorithmStr;
}
/**
* Converts fingerprint to hex
* <p/>
* Fingerprint is shown using lowercase characters. Studies have shown that humans can
* better differentiate between numbers and letters when letters are lowercase.
*
* @param fingerprint
* @return
*/
public static String convertFingerprintToHex(byte[] fingerprint) {
String hexString = Hex.toHexString(fingerprint).toLowerCase(Locale.ENGLISH);
return hexString;
}
/**
* Convert key id from long to 64 bit hex string
* <p/>
* V4: "The Key ID is the low-order 64 bits of the fingerprint"
* <p/>
* see http://tools.ietf.org/html/rfc4880#section-12.2
*
* @param keyId
* @return
*/
public static String convertKeyIdToHex(long keyId) {
long upper = keyId >> 32;
if (upper == 0) {
// this is a short key id
return convertKeyIdToHexShort(keyId);
}
return "0x" + convertKeyIdToHex32bit(keyId >> 32) + convertKeyIdToHex32bit(keyId);
}
public static String convertKeyIdToHexShort(long keyId) {
return "0x" + convertKeyIdToHex32bit(keyId);
}
private static String convertKeyIdToHex32bit(long keyId) {
String hexString = Long.toHexString(keyId & 0xffffffffL).toLowerCase(Locale.ENGLISH);
while (hexString.length() < 8) {
hexString = "0" + hexString;
}
return hexString;
}
public static SpannableStringBuilder colorizeFingerprint(String fingerprint) {
// split by 4 characters
fingerprint = fingerprint.replaceAll("(.{4})(?!$)", "$1 ");
// add line breaks to have a consistent "image" that can be recognized
char[] chars = fingerprint.toCharArray();
chars[24] = '\n';
fingerprint = String.valueOf(chars);
SpannableStringBuilder sb = new SpannableStringBuilder(fingerprint);
try {
// for each 4 characters of the fingerprint + 1 space
for (int i = 0; i < fingerprint.length(); i += 5) {
int spanEnd = Math.min(i + 4, fingerprint.length());
String fourChars = fingerprint.substring(i, spanEnd);
int raw = Integer.parseInt(fourChars, 16);
byte[] bytes = {(byte) ((raw >> 8) & 0xff - 128), (byte) (raw & 0xff - 128)};
int[] color = getRgbForData(bytes);
int r = color[0];
int g = color[1];
int b = color[2];
// we cannot change black by multiplication, so adjust it to an almost-black grey,
// which will then be brightened to the minimal brightness level
if (r == 0 && g == 0 && b == 0) {
r = 1;
g = 1;
b = 1;
}
// Convert rgb to brightness
double brightness = 0.2126 * r + 0.7152 * g + 0.0722 * b;
// If a color is too dark to be seen on black,
// then brighten it up to a minimal brightness.
if (brightness < 80) {
double factor = 80.0 / brightness;
r = Math.min(255, (int) (r * factor));
g = Math.min(255, (int) (g * factor));
b = Math.min(255, (int) (b * factor));
// If it is too light, then darken it to a respective maximal brightness.
} else if (brightness > 180) {
double factor = 180.0 / brightness;
r = (int) (r * factor);
g = (int) (g * factor);
b = (int) (b * factor);
}
// Create a foreground color with the 3 digest integers as RGB
// and then converting that int to hex to use as a color
sb.setSpan(new ForegroundColorSpan(Color.rgb(r, g, b)),
i, spanEnd, Spannable.SPAN_INCLUSIVE_INCLUSIVE);
}
} catch (Exception e) {
Log.e(Constants.TAG, "Colorization failed", e);
// if anything goes wrong, then just display the fingerprint without colour,
// instead of partially correct colour or wrong colours
return new SpannableStringBuilder(fingerprint);
}
return sb;
}
/**
* Converts the given bytes to a unique RGB color using SHA1 algorithm
*
* @param bytes
* @return an integer array containing 3 numeric color representations (Red, Green, Black)
* @throws java.security.NoSuchAlgorithmException
* @throws java.security.DigestException
*/
private static int[] getRgbForData(byte[] bytes) throws NoSuchAlgorithmException, DigestException {
MessageDigest md = MessageDigest.getInstance("SHA1");
md.update(bytes);
byte[] digest = md.digest();
int[] result = {((int) digest[0] + 256) % 256,
((int) digest[1] + 256) % 256,
((int) digest[2] + 256) % 256};
return result;
}
}
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