Objective-C

Select the S/MIME Encryption Algorithm

Demonstrates the Chilkat Email.Pkcs7CryptAlg property, which selects the underlying symmetric encryption algorithm used when an email is sent encrypted with PKCS#7 public-key (S/MIME) encryption. Possible values are aes, aes-gcm, des, 3des, and rc2; the default is aes. This example selects AES and pairs it with a 256-bit key length.

Background: S/MIME encryption is hybrid. The message body is encrypted with a fast symmetric algorithm (the one this property chooses, such as AES) using a randomly generated one-time key; then that one-time key is itself encrypted with each recipient's public key. This gives the speed of symmetric encryption with the key-distribution convenience of public-key cryptography. Modern choices like aes are strongly preferred — older options such as des and rc2 are considered weak.

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Objective-C

#import <CkoEmail.h>

//  Demonstrates the Email.Pkcs7CryptAlg property, which selects the symmetric encryption
//  algorithm used when an email is sent encrypted with PKCS#7 (S/MIME) public-key
//  encryption.  Possible values: aes, aes-gcm, des, 3des, rc2.  The default is aes.

CkoEmail *email = [[CkoEmail alloc] init];
email.Subject = @"Encrypted email";
email.Body = @"This message will be S/MIME encrypted when sent.";

//  Select AES with a 256-bit key for the symmetric encryption.
email.Pkcs7CryptAlg = @"aes";
email.Pkcs7KeyLength = [NSNumber numberWithInt:256];

NSLog(@"%@%@",@"Pkcs7CryptAlg = ",email.Pkcs7CryptAlg);
NSLog(@"%@%d",@"Pkcs7KeyLength = ",[email.Pkcs7KeyLength intValue]);