Objective-C

Set the S/MIME Encryption Key Length

Demonstrates the Chilkat Email.Pkcs7KeyLength property, which sets the key length of the symmetric algorithm used for PKCS#7 (S/MIME) encryption. The allowed values depend on Pkcs7CryptAlg: for aes use 128, 192, or 256; for 3des use 192; for des use 40; for rc2 use 40, 56, 64, or 128. The default is 128, and an unsupported algorithm/key-length combination causes encryption to fail. This example pairs AES with a 192-bit key.

Background: Key length is the size, in bits, of the secret key a symmetric cipher uses — a longer key means exponentially more possible keys and thus more resistance to brute-force attack. But length is only meaningful within a given algorithm: AES-128 is already very strong, and a key size must be one the chosen cipher actually supports, which is why Pkcs7KeyLength and Pkcs7CryptAlg have to agree.

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Objective-C

#import <CkoEmail.h>

//  Demonstrates the Email.Pkcs7KeyLength property, which sets the key length (in bits)
//  of the symmetric algorithm used for PKCS#7 (S/MIME) encryption.  The allowed values
//  depend on Pkcs7CryptAlg; for aes they are 128, 192, or 256.  The default is 128.

CkoEmail *email = [[CkoEmail alloc] init];

email.Pkcs7CryptAlg = @"aes";
email.Pkcs7KeyLength = [NSNumber numberWithInt:192];

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