A few small code cleanups for cryptography

* Remove some unused cryptographic code
* Add some notes about how Minecraft's cryptography choices have not quite survived the test of time

native/src/main/c/jni_cipher_macos.c

@@ -26,6 +26,15 @@ Java_com_velocitypowered_natives_encryption_OpenSslCipherImpl_init(JNIEnv *env,
         return 0;
     }
 
+    // But, you're saying, *why* are we using the key as the IV? After all, reusing the key as
+    // the IV defeats the entire point - we might as well just initialize it to all zeroes.
+    //
+    // You can blame Mojang. For the record, we also don't consider the Minecraft protocol
+    // encryption scheme to be secure, and it has reached the point where any serious cryptographic
+    // protocol needs a refresh. There are multiple obvious weaknesses, and this is far from the
+    // most serious.
+    //
+    // If you are using Minecraft in a security-sensitive application, *I don't know what to say.*
     CCCryptorRef cryptor = NULL;
     CCCryptorStatus result = CCCryptorCreateWithMode(encrypt ? kCCEncrypt : kCCDecrypt,
         kCCModeCFB8,

native/src/main/c/jni_cipher_openssl.c

@@ -32,6 +32,15 @@ Java_com_velocitypowered_natives_encryption_OpenSslCipherImpl_init(JNIEnv *env,
         return 0;
     }
 
+    // But, you're saying, *why* are we using the key as the IV? After all, reusing the key as
+    // the IV defeats the entire point - we might as well just initialize it to all zeroes.
+    //
+    // You can blame Mojang. For the record, we also don't consider the Minecraft protocol
+    // encryption scheme to be secure, and it has reached the point where any serious cryptographic
+    // protocol needs a refresh. There are multiple obvious weaknesses, and this is far from the
+    // most serious.
+    //
+    // If you are using Minecraft in a security-sensitive application, *I don't know what to say.*
     int result = EVP_CipherInit(ctx, EVP_aes_128_cfb8(), (byte*) keyBytes, (byte*) keyBytes,
         encrypt);
     if (result != 1) {

native/src/main/java/com/velocitypowered/natives/encryption/JavaVelocityCipher.java

@@ -48,6 +48,15 @@ public class JavaVelocityCipher implements VelocityCipher {
 
   private JavaVelocityCipher(boolean encrypt, SecretKey key) throws GeneralSecurityException {
     this.cipher = Cipher.getInstance("AES/CFB8/NoPadding");
+    // But, you're saying, *why* are we using the key as the IV? After all, reusing the key as
+    // the IV defeats the entire point - we might as well just initialize it to all zeroes.
+    //
+    // You can blame Mojang. For the record, we also don't consider the Minecraft protocol
+    // encryption scheme to be secure, and it has reached the point where any serious cryptographic
+    // protocol needs a refresh. There are multiple obvious weaknesses, and this is far from the
+    // most serious.
+    //
+    // If you are using Minecraft in a security-sensitive application, *I don't know what to say.*
     this.cipher.init(encrypt ? Cipher.ENCRYPT_MODE : Cipher.DECRYPT_MODE, key,
         new IvParameterSpec(key.getEncoded()));
   }

proxy/src/main/java/com/velocitypowered/proxy/VelocityServer.java

@@ -236,6 +236,15 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
 
     registerTranslations();
 
+    // Yes, you're reading that correctly. We're generating a 1024-bit RSA keypair. Sounds
+    // dangerous, right? We're well within the realm of factoring such a key...
+    //
+    // You can blame Mojang. For the record, we also don't consider the Minecraft protocol
+    // encryption scheme to be secure, and it has reached the point where any serious cryptographic
+    // protocol needs a refresh. There are multiple obvious weaknesses, and this is far from the
+    // most serious.
+    //
+    // If you are using Minecraft in a security-sensitive application, *I don't know what to say.*
     serverKeyPair = EncryptionUtils.createRsaKeyPair(1024);
 
     cm.logChannelInformation();

proxy/src/main/java/com/velocitypowered/proxy/crypto/EncryptionUtils.java

@@ -23,8 +23,6 @@ import com.velocitypowered.proxy.util.except.QuietDecoderException;
 import it.unimi.dsi.fastutil.Pair;
 import java.io.IOException;
 import java.math.BigInteger;
-import java.nio.ByteBuffer;
-import java.nio.ByteOrder;
 import java.nio.charset.StandardCharsets;
 import java.security.GeneralSecurityException;
 import java.security.Key;
@@ -111,42 +109,6 @@ public enum EncryptionUtils {
     }
   }
 
-  /**
-   * Generates a signature for input data.
-   *
-   * @param algorithm the signature algorithm
-   * @param base      the private key to sign with
-   * @param toSign    the byte array(s) of data to sign
-   * @return the generated signature
-   */
-  public static byte[] generateSignature(String algorithm, PrivateKey base, byte[]... toSign) {
-    Preconditions.checkArgument(toSign.length > 0);
-    try {
-      Signature construct = Signature.getInstance(algorithm);
-      construct.initSign(base);
-      for (byte[] bytes : toSign) {
-        construct.update(bytes);
-      }
-      return construct.sign();
-    } catch (GeneralSecurityException e) {
-      throw new IllegalArgumentException("Invalid signature parameters");
-    }
-  }
-
-  /**
-   * Encodes a long array as Big-endian byte array.
-   *
-   * @param bits the long (array) of numbers to encode
-   * @return the encoded bytes
-   */
-  public static byte[] longToBigEndianByteArray(long... bits) {
-    ByteBuffer ret = ByteBuffer.allocate(8 * bits.length).order(ByteOrder.BIG_ENDIAN);
-    for (long put : bits) {
-      ret.putLong(put);
-    }
-    return ret.array();
-  }
-
   public static String encodeUrlEncoded(byte[] data) {
     return MIME_SPECIAL_ENCODER.encodeToString(data);
   }
@@ -155,22 +117,6 @@ public enum EncryptionUtils {
     return Base64.getMimeDecoder().decode(toParse);
   }
 
-  /**
-   * Parse a cer-encoded RSA key into its key bytes.
-   *
-   * @param toParse     the cer-encoded key String
-   * @param descriptors the type of key
-   * @return the parsed key bytes
-   */
-  public static byte[] parsePemEncoded(String toParse, Pair<String, String> descriptors) {
-    int startIdx = toParse.indexOf(descriptors.first());
-    Preconditions.checkArgument(startIdx >= 0);
-    int firstLen = descriptors.first().length();
-    int endIdx = toParse.indexOf(descriptors.second(), firstLen + startIdx) + 1;
-    Preconditions.checkArgument(endIdx > 0);
-    return decodeUrlEncoded(toParse.substring(startIdx + firstLen, endIdx));
-  }
-
   /**
    * Encodes an RSA key as String cer format.
    *