java - 服务响应慢: Java SecureRandom &/dev/random次

Question

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Answer 1

我无法检查您的 OpenJDK 具体版本，但我可以检查 jdk6-b33 .

SecureRandom使用 SeedGenerator获取种子字节

public byte[] engineGenerateSeed(int numBytes) {
    byte[] b = new byte[numBytes];
    SeedGenerator.generateSeed(b);
    return b;
}

SeedGenerator 从 SunEntries 获取 seedSource(字符串)

String egdSource = SunEntries.getSeedSource();

SunEntries 首先尝试从系统属性 java.security.egd 获取源，如果找不到则尝试获取属性 securerandom.source 来自 java.security 属性文件，如果未找到该属性，则返回空字符串。

// name of the *System* property, takes precedence over PROP_RNDSOURCE
private final static String PROP_EGD = "java.security.egd";
// name of the *Security* property
private final static String PROP_RNDSOURCE = "securerandom.source";

final static String URL_DEV_RANDOM = "file:/dev/random";
final static String URL_DEV_URANDOM = "file:/dev/urandom";

private static final String seedSource;

static {
    seedSource = AccessController.doPrivileged(
            new PrivilegedAction<String>() {

        public String run() {
            String egdSource = System.getProperty(PROP_EGD, "");
            if (egdSource.length() != 0) {
                return egdSource;
            }
            egdSource = Security.getProperty(PROP_RNDSOURCE);
            if (egdSource == null) {
                return "";
            }
            return egdSource;
        }
    });
}

SeedGenerator检查这个值来初始化实例

// Static instance is created at link time
private static SeedGenerator instance;

private static final Debug debug = Debug.getInstance("provider");

final static String URL_DEV_RANDOM = SunEntries.URL_DEV_RANDOM;
final static String URL_DEV_URANDOM = SunEntries.URL_DEV_URANDOM;

// Static initializer to hook in selected or best performing generator
static {
    String egdSource = SunEntries.getSeedSource();

    // Try the URL specifying the source
    // e.g. file:/dev/random
    //
    // The URL file:/dev/random or file:/dev/urandom is used to indicate
    // the SeedGenerator using OS support, if available.
    // On Windows, the causes MS CryptoAPI to be used.
    // On Solaris and Linux, this is the identical to using
    // URLSeedGenerator to read from /dev/random

    if (egdSource.equals(URL_DEV_RANDOM) || egdSource.equals(URL_DEV_URANDOM)) {
        try {
            instance = new NativeSeedGenerator();
            if (debug != null) {
                debug.println("Using operating system seed generator");
            }
        } catch (IOException e) {
            if (debug != null) {
                debug.println("Failed to use operating system seed "
                              + "generator: " + e.toString());
            }
        }
    } else if (egdSource.length() != 0) {
        try {
            instance = new URLSeedGenerator(egdSource);
            if (debug != null) {
                debug.println("Using URL seed generator reading from "
                              + egdSource);
            }
        } catch (IOException e) {
            if (debug != null)
                debug.println("Failed to create seed generator with "
                              + egdSource + ": " + e.toString());
        }
    }

    // Fall back to ThreadedSeedGenerator
    if (instance == null) {
        if (debug != null) {
            debug.println("Using default threaded seed generator");
        }
        instance = new ThreadedSeedGenerator();
    }
}

如果来源是

final static String URL_DEV_RANDOM = "file:/dev/random";

或

final static String URL_DEV_URANDOM = "file:/dev/urandom"

使用 NativeSeedGenerator，在 Windows 上尝试在 Linux 上使用 native CryptoAPI 该类只是扩展 SeedGenerator.URLSeedGenerator

package sun.security.provider;

import java.io.IOException;

/**
 * Native seed generator for Unix systems. Inherit everything from
 * URLSeedGenerator.
 *
 */
class NativeSeedGenerator extends SeedGenerator.URLSeedGenerator {

    NativeSeedGenerator() throws IOException {
        super();
    }

}

并调用默认加载/dev/random的父类(super class)构造函数

URLSeedGenerator() throws IOException {
    this(SeedGenerator.URL_DEV_RANDOM);
}

因此，OpenJDK 默认使用 /dev/random，直到您未在系统属性 java.security.egd 或属性 中设置其他值安全属性文件的 securerandom.source。

如果您想使用strace 查看读取结果，您可以更改命令行并添加trace=open,read 表达式

sudo strace -o a.strace -f -e trace=open,read java class

你可以看到这样的东西(我用 Oracle JDK 6 做了测试)

13225 open("/dev/random", O_RDONLY)     = 8
13225 read(8, "@", 1)                   = 1
13225 read(3, "PK\3\4\n\0\0\0\0\0RyzB\36\320\267\325u\4\0\0u\4\0\0 \0\0\0", 30) = 30
....
....

如果您在启动过程中遇到延迟，Tomcat Wiki 的快速启动部分建议使用非阻塞熵源，如/dev/urandom

更多信息:https://wiki.apache.org/tomcat/HowTo/FasterStartUp#Entropy_Source

希望这对您有所帮助。