(.NET Core C#) RSAES-OAEP Encrypt String with AES-128 Content Encryption and SHA256

Encrypts a string using RSAES-OAEP with SHA256 and AES-128 content encryption to produce PKCS7 output (base64 encoded).

Note: This example requires Chilkat v9.5.0.67 or greater.

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

// First build a string to be encrypted
Chilkat.StringBuilder sb = new Chilkat.StringBuilder();
int i = 1;
while (i < 25) {
    sb.AppendInt(i);
    sb.Append(" the quick brown fox jumped over the lazy dog.\r\n");
    i = i + 1;
}

Debug.WriteLine(sb.GetAsString());

// The string to be encrypted looks like this:

// 1 the quick brown fox jumped over the lazy dog.
// 2 the quick brown fox jumped over the lazy dog.
// 3 the quick brown fox jumped over the lazy dog.
// 4 the quick brown fox jumped over the lazy dog.
// 5 the quick brown fox jumped over the lazy dog.
// 6 the quick brown fox jumped over the lazy dog.
// ...

// Load a digital certificate. 
// We don't need the private key for encryption.
// Only the public key is needed (which is included in a certificate).
Chilkat.Cert cert = new Chilkat.Cert();
bool success = cert.LoadFromFile("qa_data/rsaes-oaep/cert.pem");
if (success != true) {
    Debug.WriteLine(cert.LastErrorText);
    return;
}

Chilkat.Crypt2 crypt = new Chilkat.Crypt2();

// Tell the crypt object to use the certificate.
crypt.SetEncryptCert(cert);

// Indicate that we want PKI encryption (i.e. public-key infrastructure)
// to produce a CMS message (Cryptographic Message Syntax/PKCS7),
// that is be created with RSAES-OAEP padding, SHA256, and AES-128 for the
// bulk encryption.
crypt.CryptAlgorithm = "pki";
crypt.Pkcs7CryptAlg = "aes";
crypt.KeyLength = 128;
crypt.OaepHash = "sha256";
crypt.OaepPadding = true;

// Also, don't forget to be specific about the character encoding (byte representation) of the
// string to be encrypted.
crypt.Charset = "utf-8";

// Now indicate that the PKCS7 output is to be returned in the base64 encoding.
crypt.EncodingMode = "base64";

string base64Pkcs7 = crypt.EncryptStringENC(sb.GetAsString());
if (crypt.LastMethodSuccess != true) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

// Show the output
Debug.WriteLine(base64Pkcs7);

// This base64 can be copy-and-pasted into the form at http://lapo.it/asn1js/
// to verify that all the chosen algorithms were indeed used.

Debug.WriteLine("OK.");