C#

openssl smime -encrypt -des3 -in <file> <pem file>

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OpenSSL SMIME encrypt file using PEM containing a certificate. C#

bool success = false;

//  This example requires the Chilkat API to have been previously unlocked.
//  See Global Unlock Sample for sample code.

//  Load the cert from a PEM file.

Chilkat.Pem pem = new Chilkat.Pem();
//  Our particular PEM was not encrypted, so we pass an empty password.
//  Also, a private key is not needed for encryption.  The PEM used to test this example
//  happens to have a private key, but it's not actually used.
success = pem.LoadPemFile("qa_data/openssl/rsaCertAndKey.pem","");
if (success == false) {
    Debug.WriteLine(pem.LastErrorText);
    return;
}

if (pem.NumCerts == 0) {
    Debug.WriteLine("PEM does not contain any certificates.");
    return;
}

Chilkat.Cert cert = pem.GetCert(0);
if (pem.LastMethodSuccess == false) {
    Debug.WriteLine(pem.LastErrorText);
    return;
}

//  -------------------------------------------------------------------------------------
//  Duplicate this OpenSSL command:   openssl smime -encrypt -des3 -in <file> <pem file>
//  -------------------------------------------------------------------------------------
Chilkat.Crypt2 crypt = new Chilkat.Crypt2();
success = crypt.SetEncryptCert(cert);
if (success == false) {
    Debug.WriteLine(crypt.LastErrorText);

    return;
}

crypt.CryptAlgorithm = "PKI";
crypt.Pkcs7CryptAlg = "3des";
crypt.KeyLength = 168;

//  Load the file to be encrypted.
Chilkat.BinData bd = new Chilkat.BinData();
success = bd.LoadFile("qa_data/openssl/hello.txt");
if (success == false) {
    Debug.WriteLine("Failed to load the input file.");
    return;
}

//  Encrypt.
success = crypt.EncryptBd(bd);
if (success == false) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

//  The openssl smime -encrypt command produces encrypte MIME such as this:

//  MIME-Version: 1.0
//  Content-Disposition: attachment; filename="smime.p7m"
//  Content-Type: application/x-pkcs7-mime; smime-type=enveloped-data; name="smime.p7m"
//  Content-Transfer-Encoding: base64
//  
//  MIICzwYJKoZIhvcNAQcDoIICwDCCArwCAQAxggF8MIIBeAIBADBgMEoxCzAJBgNVBAYTAlVTMRYw
//  FAYDVQQKEw1MZXQncyBFbmNyeXB0MSMwIQYDVQQDExpMZXQncyBFbmNyeXB0IEF1dGhvcml0eSBY
//  MwISA9Nqgb1dH/XTDNeKzN1nR85iMA0GCSqGSIb3DQEBAQUABIIBAIQqPexjxWovgxwKV/r3HL/U
//  EP9Yozvz5hBeX5VvRZjKSi4FRw5wapElPK+4FB82hiAR9Mi3c16PvPSVkJv3l78Mv5uaaOs/OmUz
//  mIHFB6Z+l2E52BDmUVWJZTQ09vdWy6+NIRlg2R9Z1NkmZ4BZCJk6mHB/Yx03IaOxK8LnwieDMthM
//  SvxbhJnIOISN7k7ofs+/0vTXUpdQ+tlmwyVySMGQ6VMk+z4sqZJ2stacqCPtt/aiSwJ9p0OKmihf
//  3KDJceXJtavIQeA97yz1LqPvle35mmd5sBhV9qQYdTV/KJ+YM5uEZ9BHYbvMJbADFHwKzhcEY3qA
//  7T9acmEsb7NycOIwggE1BgkqhkiG9w0BBwEwFAYIKoZIhvcNAwcECERX/ZoHweSkgIIBEMmCMx49
//  zjVAnGqRaBbvzQT1hg0uQSxIJjxMxC+HSuM+eY9oSOsbrw4uIijHKH9NdOpeDsdRzg2z5EBM7AlP
//  Ht9DyPW5C2deV6RPX4F8gyExz+JUXrd+3Yb3AKTdpDkTWDmNCeO0r/YSqp518+mfU5hG8e336u51
//  HAM44FeknA8oThWsD/wUB1e8vzsatK4UXW/KSu/166V7z+VT86kd+IHa7t60U9Yp0ZXgcM5Pb5Ni
//  69Qc5MKPzom2801H5UR/WjCgsxOIjOj49sKisjRy79skrJzxY5ZG05T0dKn6KC3TjRpIEEeOyhCd
//  Nm2Y7dcW8GLMepdhWay5vePmQxmvmhbAtBprIem14NcrYeG6D5wP

//  We have the body in bd
//  Construct the header and base64 body...
Chilkat.StringBuilder sbEncryptedMime = new Chilkat.StringBuilder();

sbEncryptedMime.AppendLine("MIME-Version: 1.0",true);
sbEncryptedMime.AppendLine("Content-Disposition: attachment; filename=\"smime.p7m\"",true);
sbEncryptedMime.AppendLine("Content-Type: application/x-pkcs7-mime; smime-type=enveloped-data; name=\"smime.p7m\"",true);
sbEncryptedMime.AppendLine("Content-Transfer-Encoding: base64",true);
sbEncryptedMime.AppendLine("",true);
sbEncryptedMime.AppendLine(bd.GetEncoded("base64_mime"),true);

//  Show the result.
Debug.WriteLine(sbEncryptedMime.GetAsString());

//  or save to a file..
success = sbEncryptedMime.WriteFile("qa_output/encryptedMime.txt","utf-8",false);