(Objective-C) Extract PKCS7 Signature Digest

Demonstrates how to extract a signature digest from a PKCS7 signature.

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#import <CkoCrypt2.h>
#import <NSString.h>
#import <CkoBinData.h>
#import <CkoStringBuilder.h>

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

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

NSString *p7mFile = @"qa_data/p7m/test.pdf.p7m";
NSString *outPath = @"qa_output/test.pdf";

// First let's see if this .p7m signature can be verified, and the original file extracted.
BOOL verified = [crypt VerifyP7M: p7mFile destPath: outPath];
if (verified != YES) {
    NSLog(@"%@",crypt.LastErrorText);
    return;
}

// How many signers?
// (The NumSignerCerts property is set whenever a signature is verified.)
NSLog(@"%@%d",@"Num Signers: ",[crypt.NumSignerCerts intValue]);

// Load the .p7m into memory...
CkoBinData *pkcs7Data = [[CkoBinData alloc] init];
[pkcs7Data LoadFile: p7mFile];

// Check to see if this .p7m contains the binary bytes, or if it's
// already base64 encoded.  Get the 1st two bytes.  If the first two 
// bytes are the us-ascii values "MI", then we have base64.
CkoStringBuilder *sbBase64 = [[CkoStringBuilder alloc] init];
NSString *hexStr = [pkcs7Data GetEncodedChunk: [NSNumber numberWithInt: 0] numBytes: [NSNumber numberWithInt: 2] encoding: @"hex"];
[sbBase64 Append: hexStr];

BOOL bHaveBase64 = NO;
if ([sbBase64 ContentsEqual: @"4D49" caseSensitive: YES] == YES) {
    bHaveBase64 = YES;
    [sbBase64 Clear];
    [sbBase64 AppendBd: pkcs7Data charset: @"utf-8" offset: [NSNumber numberWithInt: 0] numBytes: [NSNumber numberWithInt: 0]];
}

// Get each signer's signature digest.
crypt.EncodingMode = @"base64";
int i = 0;
NSString *digest = 0;
while (i < [crypt.NumSignerCerts intValue]) {
    if (bHaveBase64) {
        digest = [crypt Pkcs7ExtractDigest: [NSNumber numberWithInt: i] pkcs7: [sbBase64 GetAsString]];
    }
    else {
        digest = [crypt Pkcs7ExtractDigest: [NSNumber numberWithInt: i] pkcs7: [pkcs7Data GetEncoded: @"base64"]];
    }

    if (crypt.LastMethodSuccess != YES) {
        NSLog(@"%@",crypt.LastErrorText);
        return;
    }

    NSLog(@"%@%d%@%@",@"Signer ",i + 1,@" digest = ",digest);
    i = i + 1;
}