(Objective-C) Encrypt File to PKCS7 .p7m

Objective-C example to public-key encrypt a file creating a PKCS#7 .p7m file as output. Also demonstrates how to decrypt the .p7m to recover the original file.

Chilkat Objective-C Library Downloads MAC OS X (Cocoa) Libs iOS Libs

#import <CkoCrypt2.h>
#import <CkoCert.h>
#import <NSString.h>

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

CkoCrypt2 *crypt = [[CkoCrypt2 alloc] init];

// Indicate the public-key encryption is to be used.
// Do this by setting the encryption algorithm equal 
// to "PKI" (an acroynm for public-key infrastructure).
crypt.CryptAlgorithm = @"PKI";

// Indicate the inner symmetric encryption algorithm to be used.
// possible values are "aes", "des", "3des", and "rc2".
// For this example, we'll use 256-bit AES encryption.
crypt.Pkcs7CryptAlg = @"aes";
crypt.KeyLength = [NSNumber numberWithInt:256];

// To encrypt, only a certificate w/ public key is needed.
// (The certificate w/ private key is required for decryption.)

// The LoadFromFile method can load virtually any certificate format:
// 1. DER encoded binary X.509 (.CER)
// 2. Base-64 encoded X.509 (.CER)
// 3. Cryptographic Message Syntax Standard - PKCS #7 Certificates (.P7B)
// 4. PEM format
CkoCert *encryptCert = [[CkoCert alloc] init];
BOOL success = [encryptCert LoadFromFile: @"/Users/chilkat/testData/cer/acme.cer"];
if (success != YES) {
    NSLog(@"%@",encryptCert.LastErrorText);
    return;
}

// Tell the crypt object to use the certificate for encrypting:
[crypt AddEncryptCert: encryptCert];

// Encrypt a file, producing a .p7m as output.
// The input file is unchanged, the output .p7m contains the encrypted
// contents of the input file.
NSString *inFile = @"/Users/chilkat/testData/pdf/sample.pdf";
NSString *outFile = @"/Users/chilkat/testData/p7m/sample.pdf.p7m";
success = [crypt CkEncryptFile: inFile destFile: outFile];
if (success != YES) {
    NSLog(@"%@",crypt.LastErrorText);
    return;
}

// For demonstration purposes, a different instance of the object will be used
// for decryption.
CkoCrypt2 *decrypt = [[CkoCrypt2 alloc] init];

// To decrypt, the certificate w/ private key is required.  A PFX (also known
// as PKCS#12) is a common secure container for certs and private keys.
NSString *pfxFilename = @"/Users/chilkat/testData/pfx/acme.pfx";
NSString *pfxPassword = @"secret";

// Tell the component to look in the PFX file for certs and private keys.
success = [decrypt AddPfxSourceFile: pfxFilename password: pfxPassword];
if (success != YES) {
    NSLog(@"%@",decrypt.LastErrorText);
    return;
}

// Tell the decrypt object that PKI (public key encryption) is to be used
// for decryptiong.
decrypt.CryptAlgorithm = @"PKI";
// There is no need to set the Pkcs7Alg or KeyLength because this information
// is contained within the .p7m

// Decrypt the .p7m
inFile = @"/Users/chilkat/testData/p7m/sample.pdf.p7m";
outFile = @"/Users/chilkat/testData/pdf/recovered.pdf";
success = [decrypt CkDecryptFile: inFile destFile: outFile];
if (success == NO) {
    NSLog(@"%@",decrypt.LastErrorText);
    return;
}

NSLog(@"%@",@"Success!");