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// cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");

 public byte[] sign_and_encrypt( SecretKey key ) throws InvalidKeyException, IllegalBlockSizeException, BadPaddingException {
        cipher.init(Cipher.WRAP_MODE, priv_key);
        byte [] signed = cipher.wrap(key);

        cipher.init(Cipher.ENCRYPT_MODE, their_pub_key);
        System.out.println("Signed length: " + signed.length);

        return cipher.doFinal(signed);
 }

我在 java 中对会话密钥进行签名和加密时遇到问题。带符号的 byte[] 长度为 256 字节，但doFinal底部的 只能占用大小为 245 或更小的块。

有没有办法设置添加的填充量？或者另一种在不加密两个签名切片的情况下使其工作的方法？

我得到的例外是

javax.crypto.IllegalBlockSizeException: Data must not be longer than 245 bytes
    at com.sun.crypto.provider.RSACipher.doFinal(RSACipher.java:344)
    at com.sun.crypto.provider.RSACipher.engineDoFinal(RSACipher.java:389)
    at javax.crypto.Cipher.doFinal(Cipher.java:2165)
    at Crypto.JEncrypRSA.sign_and_encrypt(JEncrypRSA.java:76)
    at Chat.Client.get_session_key(Client.java:115)
    at Chat.Client.main(Client.java:131)
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