试图了解 Java RSA 密钥大小 [英] Trying to understand Java RSA key size

问题描述

密钥生成器初始化大小为 1024，为什么打印出来的大小是 635 和 162?

The key generator was initilized with a size of 1024, so why the printed sizes are 635 and 162?

import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;

public class TEST {

    public static KeyPair generateKeyPair() throws NoSuchAlgorithmException, NoSuchProviderException {
    KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA", "BC");
    keyPairGenerator.initialize(1024);
    return keyPairGenerator.generateKeyPair();
    }

    public static void main(String[] args) throws Exception {

    KeyPair keyPair = generateKeyPair();
    RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
    RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();

    System.out.println("Size = " + privateKey.getEncoded().length);
    System.out.println("Size = " + publicKey.getEncoded().length);

    }

}

推荐答案

RSA 密钥由模数和指数组成.密钥大小是指模数中的位.因此，即使没有任何编码开销，您也需要超过 128 个字节来存储 1024 位密钥.

RSA keys are made of Modulus and Exponent. The key size refers to the bits in modulus. So even without any encoding overhead, you will need more than 128 bytes to store 1024-bit keys.

getEncoded() 返回 ASN.1 DER 编码对象.私钥甚至包含CRT参数，所以非常大.

getEncoded() returns ASN.1 DER encoded objects. The private key even contains CRT parameters so it's very large.

要获取密钥大小，请执行以下操作

To get key size, do something like this,

System.out.println("Key size = " + publicKey.getModulus().bitLength());

这里是相关的 ASN.1 对象，

Here are the relevant ASN.1 objects,

RSAPrivateKey ::= SEQUENCE {
    version           Version,
    modulus           INTEGER,  -- n
    publicExponent    INTEGER,  -- e
    privateExponent   INTEGER,  -- d
    prime1            INTEGER,  -- p
    prime2            INTEGER,  -- q
    exponent1         INTEGER,  -- d mod (p-1)
    exponent2         INTEGER,  -- d mod (q-1)
    coefficient       INTEGER,  -- (inverse of q) mod p
    otherPrimeInfos   OtherPrimeInfos OPTIONAL
}


RSAPublicKey ::= SEQUENCE {
    modulus           INTEGER,  -- n
    publicExponent    INTEGER   -- e
}

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