解密smime.p7m

Question

我正在尝试解密一个s/mime加密的附件(从Outlook/Exchange，smime.p7m)在安卓上使用Bouncycastle。

我可以在Windows上使用p7mViewer解密/查看内容。

代码，如bc-java中的ReadEncryptedMail.java：

ByteArrayInputStream inputStream = new ByteArrayInputStream(encryptedContent);
Session session = Session.getInstance(new Properties());
MimeMessage mimeMessage = new MimeMessage(session, inputStream);    
SMIMEEnveloped smimeEnveloped = new SMIMEEnveloped(mimeMessage);

结果，我在org.bouncycastle.asn1.ASN1InputStream.readLength(Unknown上得到了java.io.IOException: DER长度超过4个字节: 75 (来源:53)

我遗漏了什么？

Answer 1

经过大量的挖掘，我在bouncycastle邮件列表http://bouncy-castle.1462172.n4.nabble.com/how-to-generically-parse-a-PKCS7-object-td1467990.html上找到了“如何通用地解析PKCS7对象”

使用代码，我得到了ENVELOPEDDATA的内容类型，这使我尝试使用一个成功解析内容的CMSEnvelopedDataParser。

CMSEnvelopedDataParser cmsEnvelopedDataParser = new CMSEnvelopedDataParser(encryptedContent);
Collection recInfos = cmsEnvelopedDataParser.getRecipientInfos().getRecipients();
Iterator recipientIterator = recInfos.iterator();
if (recipientIterator.hasNext()) {
    RecipientInformation recipientInformation = (RecipientInformation) recipientIterator.next();
    byte[] contentBytes = recipientInformation.getContent(new JceKeyTransEnvelopedRecipient(privateKey));
    String content = new String(contentBytes);
}