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);