Objective-C

Get RSA Key Modulus from .cer or .key

See more Certificates Examples

Demonstrates how to get the RSA key modulus from either the certificate (.cer) or RSA key (.key). OpenSSL commands to do the same would be:

openssl x509 -inform DER -in "test.cer"  -modulus -noout 

or

openssl pkcs8 -inform DER -in​ "test.key"​ -outform PEM -passin pass:"12345​678a​"
   | openssl rsa -inform PEM -modulus -noout 

Objective-C

#import <CkoPrivateKey.h>
#import <NSString.h>
#import <CkoXml.h>
#import <CkoBinData.h>
#import <CkoCert.h>
#import <CkoPublicKey.h>

BOOL success = NO;

CkoPrivateKey *privKey = [[CkoPrivateKey alloc] init];

NSString *password = @"12345678a";
success = [privKey LoadPkcs8EncryptedFile: @"qa_data/certs/test_12345678a.key" password: password];
if (success == NO) {
    NSLog(@"%@",privKey.LastErrorText);
    return;
}

CkoXml *xml = [[CkoXml alloc] init];
[xml LoadXml: [privKey GetXml]];

// The XML contains the parts of the key in base64.
NSLog(@"%@",@"Private Key XML:");
NSLog(@"%@",[xml GetXml]);

// We can get the base64 modulus like this:
NSString *modulus = [xml GetChildContent: @"Modulus"];
NSLog(@"%@%@",@"base64 modulus = ",modulus);

// To convert to hex:
CkoBinData *binDat = [[CkoBinData alloc] init];
[binDat AppendEncoded: modulus encoding: @"base64"];
NSString *hexModulus = [binDat GetEncoded: @"hex"];
NSLog(@"%@%@",@"hex modulus = ",hexModulus);

// Now get the modulus from the cert:
CkoCert *cert = [[CkoCert alloc] init];

success = [cert LoadFromFile: @"qa_data/certs/test_12345678a.cer"];
if (success == NO) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

// The cert contains the public key, which is composed of the
// modulus + exponent (for RSA keys).
CkoPublicKey *pubKey = [[CkoPublicKey alloc] init];
[cert GetPublicKey: pubKey];

[xml LoadXml: [pubKey GetXml]];
NSLog(@"%@",@"Public Key XML:");
NSLog(@"%@",[xml GetXml]);

// Proceed in the same way as before....
modulus = [xml GetChildContent: @"Modulus"];
NSLog(@"%@%@",@"base64 modulus = ",modulus);

// To convert to hex:
[binDat Clear];
[binDat AppendEncoded: modulus encoding: @"base64"];
hexModulus = [binDat GetEncoded: @"hex"];
NSLog(@"%@%@",@"hex modulus = ",hexModulus);