I'm trying to generate a public (and private) key pair using the SecKey class from Xamarin.iOS.
The KeySize is defined to 1024 bit and this seems to work (if I change this value, the length of the result array is changing too).
I generate the keys with
SecKey.GenerateKeyPair(CreateRsaParams(), out publicKey, out privateKey);
byte[] key = publicKey.GetExternalRepresentation().ToArray()
(CreateRsaParams() is a function giving back a NSDictionary with the required data)
The problem is: I get a byte array (public key) with 140 Bytes - but depended on the key size it should have only 128 Byte - and I need a 128 Byte public key for data exchange with an other system
(by the way - using PCLCrypto is not an option for me since the project is not allowed to use this 3rd party component)
Does anyone know the problem and know a solution?
Okay, problem solved.
If anyone is facing the same problem, you can find the solution at
https://forums.developer.apple.com/thread/111109
The problem was not the key, but the wrongly formulated requirement.
Related
I'm trying to create Curve25519 keys using the KeyChain on iOS. I am aware of the existence of CryptoKit, unfortunately, that is not available for iOS 12. Is there a way to create a Curve25519 key pre CryptoKit, maybe a parameter I'm missing when generating it in the KeyChain? The code below will only generate the P-256 keys.
let attributes: [String: Any] = [
String(kSecClass): kSecClassKey,
String(kSecAttrKeyType): kSecAttrKeyTypeECSECPrimeRandom,
String(kSecAttrKeySizeInBits): 256
]
var error: Unmanaged<CFError>?
let privateKey = SecKeyCreateRandomKey(attributes as CFDictionary, &error)
print(privateKey ?? error!.takeUnretainedValue())
Apple's old core crypto lib CommonCrypto doesn't support modern curves like curve25519 and quite frankly is a total mess, littered with insecure ciphers, they aren't even clear on the actual curve equations being used.
Additionally, although CryptoKit supports curve25519 for key exchange, it's still limited, for example, you cannot use the "Secure Enclave" to generate curve25519 keys, only P-256, which is likely backdoored (just look at the curve co-efficients), despite all financial institutions seemingly loving it.
Ultimately a curve25519 private key is just a large (2^256) number (though it is "clamped" before use), so if you just need to generate keys, you can do this with SecRandomCopyBytes.
Though, if as I suspect you want to do some X25519 KEX or EdDSA signature over 25519, then just use libsodium. It's the goto library for NaCl, there is a really great interface in Swift written by the original libsodium author, called swift-sodium, I've used it and it's great. It also supports iOS 12+.
Generating keys in libsodium for curve25519 is as simple as:
import Sodium
let sodium = Sodium()
let curve25519KeyPair = sodium.box.keyPair()
let privateKey = curve25519KeyPair!.secretKey
let publicKey = curve25519KeyPair!.publicKey
You can then manually store in KeyChain.
Shout if you need further help, and good choice using 25519.
I want to ssl public key pinning in swift, I read lot of examples how to do that, last think who I can't find is How to compare two public keys in SecKey object format.
Example:
let serverPublicKey = SecTrustCopyPublicKey(secTrust) /*return SecKey object from actual SecTrust*/
let clientPublicKey = getLocalPublicKeyFromDer() /*return SecKey from .der local*/
how to compare them? At now I do that and it works:
if(serverPublicKey! as AnyObject).isEqual(clientPublicKey){
/*Key is the same, pinning OK!*/
}
find it way on gitHub: https://github.com/teamcarma/IOS-AlamofireDomain/blob/master/Source/ServerTrustPolicy.swift
but is cast to AnyObject a good idea? How to work isEqual on casted SecKey? Can any explain me?
ps.
Another idea is getting base64 from SecKey - I try and it also works, but it require a KeyChain temp operations and look no profesional.
Cited from the headers:
"Most SecKeychainItem functions will work on an SecKeyRef."*
You may cast SecKeyRef to a SecKeychainItem. If this is a valid operation (that is, the key is a keychain item), you may apply function
SecKeychainItemCreatePersistentReference
and get a CFData object, filled with attributes and data. Then check with memcpyon the bytes or cast it to a NSData object and check with isEqualToData. Don't forget to release the CFData object.
Edit
On iOS, as far as I known, the only reliable approach is to copy the data (or secret) into the keychain, using a temporary key, so that you can find it again, and then extract the data. It's cumbersome, but if you just implement it in a minimalistic way, it should not take more than 30 lines of code. I have a working example.
I The usual disclaimer: Use this at your own risk, and always be careful with security stuff.
iOS10 added:
CFDataRef _Nullable SecKeyCopyExternalRepresentation(SecKeyRef key, CFErrorRef *error)
so you can now create two Data (NSData) objects, then compare those.
Have a look at this answer for just getting the NSData: Can I get the modulus or exponent from a SecKeyRef object in Swift?
You can then compare the two NSData instances using isEqualToData:
I don't have expereince in the domain, but if they are two strings (irrespectiveof their content), you would basically do a simple check:
if(string1 == string2)
{
//condition logic
}
I'm trying to do RSA2048 in iOS and am following the example codes from Apple and also this question RSA implementations in Objective C. I have tested on iPhone 5c with iOS 8.4.1, but the sample codes fail at decryption with private key, with error code -9809 (An underlying cryptographic error was encountered), even though encryption with public key. I understand the basic approach is to generate an RSA key pair, secure them in keychain and use public key ref to encrypt and private key to decrypt. I'm completely lost why decryption shall fail, and not always, there are times when decryption succeeded.
Full codes can be found at https://gist.github.com/aceisScope/372e6d6f92650ce03624. The decryption part that throws an error is below, where from time to time status = -9809, and other times it works and returns 0:
status = SecKeyDecrypt(privateKey,
PADDING,
cipherBuffer,
cipherBufferSize,
plainBuffer,
&plainBufferSize
);
I have also set a check that if such key pair has already generated, next time encryption/decryption is called, it will directly using the already-generated-and-stored key pair from key chain without generating a new pair.
Update:
I came across this post iPhone Public-Key Encryption SecKeyEncrypt returns error 9809 (errSSLCrypto) which found out wrong cipher buffer size may cause -9809 error to encryption. Yet even if I make sure both the cipher buffer size in encryption and plain buffer size in decryption is the same as key block size and private key block size, encryption always works but with decryption failing from time to time.
I found the problem. By the end of encryption, when converting cipher buffer to NSData, in the following code
NSMutableData *data=[[NSMutableData alloc] init];
[data appendBytes:cipherBuffer length:strlen( (char*)cipherBuffer ) + 1];
the length is not correct. It should be the size of the cipher buffer, which is the same as key block size.
So after changing it to
NSData *data = [NSData dataWithBytes:cipherBuffer length:cipherBufferSize];
decryption works now.
From what I can tell looking through the various padding values for the SecKeyEncrypt method in Apple's security framework, it does not support OAEP padding with a SHA512 hash digest. In fact, I can't seem to determine if the SecKeyEncrypt method does any sort of hashing/masking of each block during the CBC process.
Herein lies my problem. All my other platforms (PHP, Android, .NET) use RSA with OAEP padding and a SHA512 digest.
For example: In C# we can use BouncyCastle's OaepEncoding class which accepts any Digest and performs the hash/mask operation during the block cipher encryption process. In php, the phpseclib project provides the same functionality.
And finally, my question... can this same functionality be achieved on iOS by somehow using a hybrid of "manual" hashing and using SecKeyEncrypt? Or am I missing something much more obvious here.
Cheers!
EDIT: I think I could probably hash/mask each block by porting the bouncy castle code and then pass the new byte array to SecKeyEncrypt for encrpytion, but that begs the question, does SecKeyEncrypt do that already using some other hashing algo internally?
As of iOS 10.0, the .rsaEncryptionOAEPSHA512 option has been added as a SecKeyAlgorithm.
Swift 4
let attributes: [String: Any] = [ ... ]
let pk = SecKeyCreateRandom(attributes as CFDictionary, nil)!
let pub = SecKeyCopyPublicKey(pk)!
let message = "Encrypt me".data(using: .utf8)!
var error: Unmanaged<CFError>?
let cipherText = SecKeyCreateEncryptedData(pub, .rsaEncryptionOAEPSHA512, message as CFData, &error)
It appears this is not possible native to the Security framework for iOS. I have had a ton of issues getting OAEP RSA encryption to work properly cross platform.
However, I did just hear from a third party library provider, Chillkat, that they are adding support for this. See: http://www.chilkatforum.com/questions/7778/ios-rsa-encryption-using-oaep-sha512
EDIT: I installed Chilkat's library and had it working in minutes.
I'm trying to implement decryption of a PGP file on an iPad. I set up some test .txt files which I then encrypted via PGP desktop.
I've imported the private key of the certificate used to encrypt the document, using SecPKCS12Import, then SecIdentityCopyPrivateKey() from the resulting SecIdentityRef.
If I test encrypting and decrypting a simple string in Objective C, using the public and private key of the cert, that works perfectly.
Now that I'm trialling the actual PGP decryption, I'm a bit stumped... Reading the text from the .pgp file, I get:
-----BEGIN PGP MESSAGE-----
Version: 10.1.1.10
qANQR1DBwEwDraQm2Kxa5GkBB/4yLebeLk10C2DVvHpQL20E0DThhgQlTasXo+YJ
pLp5Ig2hHu4Xx0m74D3vfyWpA2XQA02TMAHO9lhNfkE234c/ds05D1UyQkJEoqW+
joEcbRT5rlGN3qrMf1FXv8/01EHH0dgeD6mAkkDeDEorIirYHCF6+QVkedaphZLs
c63GmcikzkWZT/vv20ICL3Ys0DaC3P9zu0T1GtjkmQ062kaTab/VBJnQrsY/y1JU
ypmbW9bbFeZMcAqXHMqpjw49K5UluIJaDbRNAjIvHTFLNuOYWVJM6FcMs5p6xqvZ
ltizeKAjr1B1h4DvbQaqdO6/OAb+dGr7fJoIHEszDsJbW1cc0lUBitrxKHrPGovF
1uEW+3glA3SopveWB4GkKzcYlbqT5y1p/gQNwY8yuZr/6iF1hyF9mx/hU/+xjOMB
og3sGX4npcQegsAMw2y+zz9kJ9a6jlteNufi
=d2Fq
-----END PGP MESSAGE-----
I know that I need to get the random one-time key, that PGP used to encrypt the file, from the data in the file. I know that to do that, I need to use SecKeyDecrypt with the private key, to obtain the one-time AES key. Once I have that key, I can then decrypt the rest of the data.
The part I'm having problems with is which part of the data to feed into SecKeyDecrypt. How is the PGP file setup - is the first 128 chars the AES key? Unless my understanding is wrong, I need to get that out separately from the data.
If I run, say, the first 128 chars as a void through the SecKeyDecrypt function: (after stripping the BEGIN PGP MESSAGE lines)
size_t dataLength = [theKey length];
size_t outputLength = MAX(128, SecKeyGetBlockSize(privateKeyRef));
void *outputBuf = malloc(outputLength);
OSStatus err;
err = SecKeyDecrypt(privateKeyRef, kSecPaddingNone,//PKCS1,
(uint8_t *)theKey, dataLength,
outputBuf, &outputLength);
if (err) {
NSLog(#"something went wrong...err = %ld", err);
}
I get this:
MRªh6∞bJ˘e£t*˝ã=ŒA¢Òt‘ŸY±éÿAÃîâG
Îfi≠$b≈tâç`yxk=uHªqu-,–dïn^™È\›5±tb.‡€Kñ⁄≤sΩw–ïʃkafS˘À*Æô竡rAyv)fi]wOrµKz^ªq“à∑öΓı*r<+l˝Äo∑›g≠¶/÷eÔ&€PÒRåêM¶Ñ|Q$á6În^võ¬∏·h(ƒß•R≤(flò(*•Aa
I don't know what encoding this is, but trying to get it from the outputBuf into a string never works 100%. It seems to get modified no matter what encoding I pass it. If I pass it to NSData first, I can get the original string back.
NSData *keyData = [NSData dataWithBytesNoCopy:outputBuf length:outputLength];
NSString *keyFromData = [[NSString alloc] initWithBytes:[keyData bytes] length:[keyData length] encoding:NSASCIIStringEncoding];
I then try to pass that key to an AES256DecryptWithKey class, providing it with the remaining data from the PGP file, after the first 128 chars.
NSData *cipherText = [[NSData alloc]initWithData:[[bodyPart objectAtIndex:1] dataUsingEncoding:NSUTF8StringEncoding]];
NSData *plain = [[NSData alloc] initWithData:[cipherText AES256DecryptWithKey:keyFromData]];
NSLog(#"after decrypting = %#", [[NSString alloc] initWithData:plain encoding:NSUTF8StringEncoding]);
Problem:
The resulting data 'plain' prints as <> i.e. empty. My problem is I don't even think I know how to grab the key from the PGP file.
Can anyone explain to me the PGP file setup? What part is the 'key' if it is in fact separate from the data at all? Is it always the same length/ same position? If it's NOT separate then I don't know how I'd be able to grab it at all. I think the rest would work fine. I'm not getting any errors or crashes, it's just NOT the right key and/or data I'm passing for AES decryption, I suspect probably a combination of string encoding error and not grabbing the right amount for the AES key/ right combination.
Note -
I created 3 different text files and ran them through the PGP process. Inspecting them, they all started with the same 24 characters (qANQR1DBwEwDraQm2Kxa5GkB). Even if I pass these 24 through the decryption, it doesn't work, and I was under the impression that the AES key PGP used was different for every single document. Did I get that wrong?
Thanks for any step in the right direction!
Edited to add:
Just noticed partly my mistake - AES of 128 requires 16 bits, so either way I am taking the wrong amount by using 128 characters, stupid mistake, think I've been looking at this too long... Swapped it out and didn't work. Any decryption I do is resulting in the '⁄Ĉ¢ï¡0M¶È2Cˆ¿©gUú¨6iîΩ`&<%Jœv£¯nRb∆:(–%' type result, which to me implies I've done something wrong OR need to do something further with encoding.
Read RFC 4880. That file is an ASCII-Armored collection of PGP packets. There are 1 or more packets that contain the symmetric key needed to decrypt the actual message, each of the symmetric key packets is encrypted with the public key of a recipient. Only people who possess the right private key can decrypt the symmetric key packet and then use that symmetric key to decrypt the rest of the message.
The AES key is indeed different.
It is randomly selected, and the encrypted with the public key system (RSA, typically).
Pub key has costs and limitations that make it unattractive to use for bulk.
You might want to look at the NetPGP, which is C code under the
BSD license, which means you can incorporate it or modify it
without encumbering your app or upsetting Apple in any way.
(Of course, contributions of source code or money would be
appreciated by the project. I'm not affiliated with them.)
The OpenPGP standard is a lot of work to implement.
Even once an implementation works, there are countless
ways in which it can be insecure.