OAEP uses a separate hash invocation to hash a (usually empty) label as well as a parameter to MGF1 (mask generation function), used for most of the OAEP padding. The hash doesn’t have that much impact on the security of OAEP, and for that reason it may be left to this default. Most libraries however … Read more
A secure RSA encryption is implemented with an appropriate padding scheme, which includes some randomness. See PKCS#1 or OAEP for more details. The RSA encryption encrypts message padded with ‘0’s and a string of random bit. In the process, the random string is “hidden” in the ciphertext by cryptographic hashing and XORing. On decryption, the … Read more
use of undeclared identifier ‘publicTag’ The publicTag is just some unique identifier added to the Keychain items. In the CryptoExercise sample project it is defined as #define kPublicKeyTag “com.apple.sample.publickey” static const uint8_t publicKeyIdentifier[] = kPublicKeyTag; NSData *publicTag = [[NSData alloc] initWithBytes:publicKeyIdentifier length:sizeof(publicKeyIdentifier)]; Cast of an indirect pointer to an Objective-C pointer to ‘CFTypeRef ‘ (aka … Read more
You cannot use an RSA encryption decryption on more than approx 128 bytes at a time. You must split up the data and do it in a loop pretty much writing the bytes to String/Array as you go. If your only problem is the size of the data, you probably don’t have much more to … Read more
A common mistake is to try to decrypt using the public key.
To Generate Private Key openssl genrsa -out privatekey.pem 2048 To Sign openssl dgst -sha256 -sign privatekey.pem -out data.txt.signature data.txt To Generate The Public Key dgst -verify requires the public key openssl rsa -in privatekey.pem -outform PEM -pubout -out publickey.pem To Verify openssl dgst -sha256 -verify publickey.pem -signature data.txt.signature data.txt In case of success: prints “Verified … Read more
I believe that the issue may be that the key is not marked as exportable. There is another constructor for X509Certificate2 that takes an X509KeyStorageFlags enum. Try replacing the line: X509Certificate2 x = new X509Certificate2(@”C:\temp\certs\1\test.pfx”, “test”); With this: X509Certificate2 x = new X509Certificate2(@”C:\temp\certs\1\test.pfx”, “test”, X509KeyStorageFlags.Exportable);
Let’s assume that e is small (that’s the common case; the Traditional public exponent is 65537). Let’s also suppose that ed = 1 mod phi(n), where phi(n) = (p-1)(q-1) (this is not necessarily the case; the RSA requirements are that ed = 1 mod lcm(p-1,q-1) and phi(n) is only a multiple of lcm(p-1,q-1)). Now you … Read more
I struggled a lot with the same problem and finally found a solution. My problem was that I needed to use both an external private and public key for encrypting/decrypting data in an iOS app and didn’t want to use the keychain. It turns out you also need a signed certificate for the iOS security … Read more
You are right, the RSA signature size is dependent on the key size, the RSA signature size is equal to the length of the modulus in bytes. This means that for a “n bit key”, the resulting signature will be exactly n bits long. Although the computed signature value is not necessarily n bits, the … Read more