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use a secure algorithm to generate image urls so that only server-side generated urls can be used

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Athou
2026-06-13 11:21:11 +02:00
parent 831ca599b8
commit c43644861f
1 changed files with 50 additions and 19 deletions
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69
commafeed-server/src/main/java/com/commafeed/backend/feed/ImageProxyUrl.java
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@@ -1,37 +1,68 @@
package com.commafeed.backend.feed;
import org.apache.hc.client5.http.utils.Base64;
import java.nio.charset.StandardCharsets;
import java.security.SecureRandom;
import java.util.Arrays;
import java.util.Base64;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.GCMParameterSpec;
import com.google.common.primitives.Bytes;
import lombok.experimental.UtilityClass;
@UtilityClass
public class ImageProxyUrl {
private static final SecretKey KEY;
private static final SecureRandom SECURE_RANDOM = new SecureRandom();
private static final int GCM_IV_LENGTH = 12;
private static final int GCM_TAG_LENGTH = 128;
static {
try {
KeyGenerator keyGen = KeyGenerator.getInstance("AES");
keyGen.init(256, SECURE_RANDOM);
KEY = keyGen.generateKey();
} catch (Exception e) {
throw new IllegalStateException("Failed to generate AES key", e);
}
}
public static String encode(String url) {
return Base64.encodeBase64String(rot13(url).getBytes());
try {
byte[] iv = new byte[GCM_IV_LENGTH];
SECURE_RANDOM.nextBytes(iv);
Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
cipher.init(Cipher.ENCRYPT_MODE, KEY, new GCMParameterSpec(GCM_TAG_LENGTH, iv));
byte[] encrypted = cipher.doFinal(url.getBytes(StandardCharsets.UTF_8));
byte[] combined = Bytes.concat(iv, encrypted);
return Base64.getUrlEncoder().withoutPadding().encodeToString(combined);
} catch (Exception e) {
throw new IllegalStateException("Failed to encode URL", e);
}
}
public static String decode(String code) {
return rot13(new String(Base64.decodeBase64(code)));
}
try {
byte[] combined = Base64.getUrlDecoder().decode(code);
private static String rot13(String msg) {
StringBuilder message = new StringBuilder();
byte[] iv = Arrays.copyOfRange(combined, 0, GCM_IV_LENGTH);
byte[] encrypted = Arrays.copyOfRange(combined, GCM_IV_LENGTH, combined.length);
for (char c : msg.toCharArray()) {
if (c >= 'a' && c <= 'm') {
c += 13;
} else if (c >= 'n' && c <= 'z') {
c -= 13;
} else if (c >= 'A' && c <= 'M') {
c += 13;
} else if (c >= 'N' && c <= 'Z') {
c -= 13;
}
message.append(c);
Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
cipher.init(Cipher.DECRYPT_MODE, KEY, new GCMParameterSpec(GCM_TAG_LENGTH, iv));
byte[] decrypted = cipher.doFinal(encrypted);
return new String(decrypted, StandardCharsets.UTF_8);
} catch (Exception e) {
throw new IllegalStateException("Failed to decode URL", e);
}
return message.toString();
}
}