(Objective-C) Decrypt S/MIME and Verify S/MIME Signatures

Objective-C example to decrypt S/MIME and verify S/MIME signatures. The S/MIME is unwrapped to get the original MIME prior to signing/encrypting.

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#import <CkoMime.h>
#import <CkoCert.h>

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

CkoMime *mime = [[CkoMime alloc] init];

// Load an S/MIME message from a file:
BOOL success = [mime LoadMimeFile: @"signedMime.txt"];
if (success != YES) {
    NSLog(@"%@",mime.LastErrorText);
    return;
}

// The ContainsEncryptedParts/ContainsSignedParts methods
// can be called to determine if the MIME is encrypted and/or signed:
BOOL isEncrypted = [mime ContainsEncryptedParts];
BOOL isSigned = [mime ContainsSignedParts];

// We don't want the "unwrap extras".  You'll see what those
// are in a few moments...
mime.UnwrapExtras = NO;

// To verify the signature, call UnwrapSecurity.  This will
// verify the signature(s) and decrypt the S/MIME and restore
// the MIME to the unsigned/unencrypted state.
// The results of what was found are present in the MIME object's
// properties, as well as extra header fields that are added
// to the unwrapped MIME.
success = [mime UnwrapSecurity];
if (success != YES) {
    // UnwrapSecurity returns YES if all signatures were
    // verified and all parts decrypted.
    NSLog(@"%@",mime.LastErrorText);
    return;
}

// The mime.UnwrapExtras property controls whether or not
// these additional fields are added to the unwrapped MIME:
// 
// X-NumPartsSigned: 1
// X-SignaturesValid: yes
// X-NumPartsEncrypted: 1
// X-Decrypted: no
// 
// The X-NumPartsSigned/X-SignaturesValid headers are added
// if the MIME was signed.  
// 
// The X-NumPartsEncrypted/X-Decrypted headers are added
// if the MIME was encrypted.
// 

// If the MIME was signed, get the certificate used for signing.
if (isSigned == YES) {
    // The NumSignerCerts property indicates how many certificates
    // were used for signing.  This example will assume the value is 1.
    // To get the 1st signer cert, call GetSignerCert with an index of 0:
    CkoCert *signerCert = [mime GetSignerCert: [NSNumber numberWithInt: 0]];
    if (mime.LastMethodSuccess == YES) {
        NSLog(@"%@%@",@"**** Signer Cert: ",signerCert.SubjectCN);

    }

}

// If the MIME was encrypted, get the certificate used for encryption:
if (isEncrypted == YES) {
    // The NumEncryptCerts property indicates how many certificates
    // were used for encrypting.  This example will assume the value is 1.
    // To get the 1st encrypt cert, call GetEncryptCert with an index of 0:
    CkoCert *encryptCert = [mime GetEncryptCert: [NSNumber numberWithInt: 0]];
    if (mime.LastMethodSuccess == YES) {
        NSLog(@"%@%@",@"**** Encrypt Cert: ",encryptCert.SubjectCN);

    }

}

// Display the unwrapped MIME:
NSLog(@"%@",[mime GetMime]);

// Save the unwrapped MIME to a file:
success = [mime SaveMime: @"unwrappedMime.txt"];