gistfile1.m

// ...import OpenSSL headers...

DSA* dsa = DSA_new();

const char *privateKey = [[NSString stringWithContentsOfFile: @"/private.pem"] UTF8String];

BIO* bio = BIO_new_mem_buf((void*)privateKey, -1);

PEM_read_bio_DSAPrivateKey(bio, &dsa, NULL, NULL);

BIO_vfree(bio);

// * * *.

NSData* digest = [[@"John Appleseed" dataUsingEncoding: NSUTF8StringEncoding] SHA1Data];

unsigned char signature[100];

unsigned int signatureLength;

if(!DSA_sign(NID_sha1, [digest bytes], [digest length], signature, &signatureLength, dsa))
{
  NSLog(@"SIGNING FAILED");
}

DSA_free(dsa);

NSString* serial = [[[NSData dataWithBytes: signature length: signatureLength] base32String] stringByReplacingOccurrencesOfString: @"=" withString: @""];