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如何检查pdf的签名

首先这里有一个已经签名的pdf文件，通过pdf软件可以看到文件的数字签名。
图1为签名后的文件，图2为签名后文件被篡改。

下面就是如何代码检查这里pdf文件的签名
1.引入依赖

 <dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency><!-- https://mvnrepository.com/artifact/com.itextpdf/itextpdf --><dependency><groupId>com.itextpdf</groupId><artifactId>itextpdf</artifactId><version>5.5.13.3</version></dependency><dependency><groupId>org.bouncycastle</groupId><artifactId>bcprov-jdk15on</artifactId><version>1.70</version></dependency><dependency><groupId>org.bouncycastle</groupId><artifactId>bcpkix-jdk15on</artifactId><version>1.70</version></dependency>

2. 编写检查签名的方法

import com.itextpdf.text.pdf.AcroFields;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.security.PdfPKCS7;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;import java.io.IOException;
import java.security.GeneralSecurityException;
import java.security.Principal;
import java.security.Provider;
import java.security.Security;
import java.security.cert.X509Certificate;
import java.util.Calendar;
import java.util.List;/*** pdf文件签名检查*/
public class PdfDigitalSignatureCheck {private static final Logger LOGGER = LoggerFactory.getLogger(PdfDigitalSignatureCheck.class);public static final boolean verifySignature(PdfReader pdfReader)throws GeneralSecurityException, IOException {boolean valid = false;AcroFields acroFields = pdfReader.getAcroFields();List<String> signatureNames = acroFields.getSignatureNames();if (!signatureNames.isEmpty()) {for (String name : signatureNames) {if (acroFields.signatureCoversWholeDocument(name)) {//设定签名提供者Provider provider=Security.getProvider(BouncyCastleProvider.PROVIDER_NAME);if(provider==null){provider=new BouncyCastleProvider();Security.addProvider(provider);}PdfPKCS7 pkcs7 = acroFields.verifySignature(name);valid = pkcs7.verify();String reason = pkcs7.getReason();Calendar signedAt = pkcs7.getSignDate();X509Certificate signingCertificate = pkcs7.getSigningCertificate();Principal issuerDN = signingCertificate.getIssuerDN();Principal subjectDN = signingCertificate.getSubjectDN();LOGGER.info("valid = {}, date = {}, reason = '{}', issuer = '{}', subject = '{}'",valid, signedAt.getTime(), reason, issuerDN, subjectDN);break;}}}return valid;}/*** 验证签名** @param name* @return* @throws IOException* @throws GeneralSecurityException*/public static boolean validate(String name)throws IOException, GeneralSecurityException {PdfReader reader = new PdfReader(name);boolean isSign = verifySignature(reader);return isSign;}}

3. 编写测试用例,并执行，可以看到数字证书相关信息。

如果有多个签名，则会显示多个签名

    @Testvoid pdfDigitalSignatureCheck() throws IOException, GeneralSecurityException {System.out.println("-----------数字签名检查------------");String[] files = {"D:\\test3\\test1_sign.pdf", "D:\\test3\\test1.pdf","D:\\test3\\test1_sign_wrapper.pdf"};for (String file : files) {boolean validate = PdfDigitalSignatureCheck.validate(file);log.info("{} 是否签名:{}", file, validate);}}

备注: test1_sign.pdf 为已签名文件，test1.pdf为原始未签名文件，test1_sign_wrapper.pdf为签名后更改过的文件（模拟签名后文件被篡改）

遇到的问题

签名设定

如果你的签入使用的BouncyCastleProvider，那么你的签名检查也应该使用BouncyCastleProvider，否则可能会报错。