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使用C从p7+p8文件获取PEM#

pkcs#7 pem bouncycastle cryptography c#

Martijn Kooij · 技术社区 · 6 年前

简介

我正在将Java库转换为.Net。

该库是多态化名解密的一个实现,将在荷兰用于解密欧洲eIDAS电子识别服务领域的“BSNk”。

下一步是使.Net库真正可供荷兰公司使用,这也是我过去两周一直在努力的方向。

算法使用PEM文件中的椭圆曲线作为计算的一部分。但是客户机(库的用户)将以p7和p8文件的形式接收这些数据,您可以将它们转换/提取/解码(?)为PEM数据。

问题

如何将te p7+p8文件转换为C#中的PEM字符串?

下面没有列出,但我也尝试过使用SignedCms和EnvelopedCms来实现这一点,但是(对我来说)从中得到的只是无法理解的错误。我在密码学方面没有太多的经验,但在过去的几周里学到了不少。

代码

public static string ConvertToPem(string p7File, string p8File)
{
    var p7Data = File.ReadAllBytes(p7File);
    var p8Data = File.ReadAllBytes(p8File);

    // Java version gets the private key like this:
    // KeyFactory.getInstance("RSA").generatePrivate(new PKCS8EncodedKeySpec(bytesArray));
    var privateKey = PrivateKeyFactory.CreateKey(p8Data);

    var parser = new CmsEnvelopedDataParser(p7Data);
    var recipients = parser.GetRecipientInfos().GetRecipients().OfType<RecipientInformation>();
    var recipientInformation = recipients.First();

    //Java version gets the message like this:
    //final byte[] message = keyInfo.getContent(new JceKeyTransEnvelopedRecipient(key).setProvider("BC"));

    var keyInfo = (KeyTransRecipientInformation)recipientInformation;
    var message = keyInfo.GetContent(privateKey);

    return Encoding.ASCII.GetString(message);
}

更新日期:8-10-2018

openssl cms -decrypt -inform DER -in dv_keys_ID_D_oin.p7 -inkey privatep8.key -out id.pem

(我也试过用PEM代替DER,但没有效果。文件在GitHub repo中)

更新日期:9-10-2018

openssl pkcs8 -inform der -outform pem -in private.p8 -out private-p8.pem -topk8 -nocrypt

在我的项目中,您可以看到此代码作为单元测试被使用并失败。该项目还包括匹配p7、p8和PEM文件进行测试。

https://github.com/BramvanPelt/PPDecryption

我的工作进行中版本可以在这里找到: https://github.com/MartijnKooij/PolymorphicPseudonymisation

2 回复 | 直到 6 年前

Carl in 't Veld 6 年前

最后我成功地解密了这个消息;看起来BouncyCastleAPI忽略了SHA-256OAEP指令,并坚持使用SHA-1OAEP,这导致了填充异常。此外,Microsoft API还利用 X509Certificate2 只支持 RsaCryptoServiceProvider 据我所知,有SHA-1 OAEP支持。一个人需要更新的 RsaCng https://github.com/dotnet/corefx )以及bc csharp( https://github.com/bcgit/bc-csharp

下面的c代码将解密消息;使用Microsoft API:

// Read the RSA private key:
var p8Data = File.ReadAllBytes(@"resources\private.p8");    
CngKey key = CngKey.Import(p8Data, CngKeyBlobFormat.Pkcs8PrivateBlob);
var rsaprovider = new RSACng(key);

// Process the enveloped CMS structure:
var p7Data = File.ReadAllBytes(@"resources\p7\ID-4.p7");
var envelopedCms = new System.Security.Cryptography.Pkcs.EnvelopedCms();
envelopedCms.Decode(p7Data);
var recipients = envelopedCms.RecipientInfos;
var firstRecipient = recipients[0];

// Decrypt the AES-256 CBC session key; take note of enforcing OAEP SHA-256:
var result = rsaprovider.Decrypt(firstRecipient.EncryptedKey, RSAEncryptionPadding.OaepSHA256);

// Build out the AES-256 CBC decryption:
RijndaelManaged alg = new RijndaelManaged();
alg.KeySize = 256;
alg.BlockSize = 128;
alg.Key = result;

// I used an ASN.1 parser (https://lapo.it/asn1js/) to grab the AES IV from the PKCS#7 file.
// I could not find an API call to get this from the enveloped CMS object:
string hexstring = "919D287AAB62B672D6912E72D5DA29CD"; 
var iv = StringToByteArray(hexstring);
alg.IV = iv;
alg.Mode = CipherMode.CBC;
alg.Padding = PaddingMode.PKCS7;

// Strangely both BouncyCastle as well as the Microsoft API report 406 bytes;
// whereas https://lapo.it/asn1js/ reports only 400 bytes. 
// The 406 bytes version results in an System.Security.Cryptography.CryptographicException 
// with the message "Length of the data to decrypt is invalid.", so we strip it to 400 bytes:
byte[] content = new byte[400];
Array.Copy(envelopedCms.ContentInfo.Content, content, 400);
string decrypted = null;
ICryptoTransform decryptor = alg.CreateDecryptor(alg.Key, alg.IV);
using (var memoryStream = new MemoryStream(content)) {
    using (var cryptoStream = new CryptoStream(memoryStream, alg.CreateDecryptor(alg.Key, alg.IV), CryptoStreamMode.Read)) {
        decrypted = new StreamReader(cryptoStream).ReadToEnd();
    }
}

实施 StringToByteArray 具体如下:

public static byte[] StringToByteArray(String hex) {
    NumberChars = hex.Length;
    byte[] bytes = new byte[NumberChars / 2];
    for (int i = 0; i < NumberChars; i += 2)
        bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
    return bytes;
}

bartonjs 6 年前

您应该能够通过.NET 4.7.2实现您的目标:

using (CngKey key = CngKey.Import(p8Data, CngKeyBlobFormat.Pkcs8PrivateBlob))
{
    // The export policy needs to be redefined because CopyWithPrivateKey
    // needs to export/re-import ephemeral keys
    key.SetProperty(
        new CngProperty(
            "Export Policy",
            BitConverter.GetBytes((int)CngExportPolicies.AllowPlaintextExport),
            CngPropertyOptions.Persist));

    using (RSA rsa = new RSACng(key))
    using (X509Certificate2 cert = new X509Certificate2(certData))
    using (X509Certificate2 certWithKey = cert.CopyWithPrivateKey(rsa))
    {
        EnvelopedCms cms = new EnvelopedCms();
        cms.Decode(p7Data);
        cms.Decrypt(new X509Certificate2Collection(certWithKey));

        // I get here reliably with your reference documents
    }
}