How Do I PInvoke Into CommonCrypto CCKeyDerivationPBKDF? - xamarin

Question

I am attempting to PInvoke into the CCKeyDerivationPBKDF here.
The method signature looks like this:
int
CCKeyDerivationPBKDF( CCPBKDFAlgorithm algorithm, const char *password, size_t passwordLen,
const uint8_t *salt, size_t saltLen,
CCPseudoRandomAlgorithm prf, uint rounds,
uint8_t *derivedKey, size_t derivedKeyLen)
__OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_NA);
Currently I am attempting this:
[DllImport(ObjCRuntime.Constants.libSystemLibrary, EntryPoint = "CCKeyDerivationPBKDF")]
public extern static void CCKeyCerivationPBKDF(int algorithm, string password, int passwordLen,
string salt, int saltLen, int prf, int rounds, out byte[] derivedKey, int derivedKeyLength);
and am getting the error:
malloc: *** error for object 0xb9374fc61e8f9d1e: pointer being freed was not allocated
This is my first attempt to PInvoke something. I'm fairly certain that my signature is probably way off. What does it need to be?

Answer 1

You are getting the pointer being freed was not allocated error due to the out flag on the derivedKey parameter, just pass it as an IntPtr (byte[]) and Mono will marshall it correctly:
CCKeyCerivationPBKDF signature:
[DllImport(ObjCRuntime.Constants.libSystemLibrary, EntryPoint = "CCKeyDerivationPBKDF")]
public extern static int CCKeyCerivationPBKDF(
int algorithm,
string password,
nint passwordLen,
string salt,
nint saltLen,
UInt32 prf,
int rounds,
byte[] derivedKey,
int derivedKeyLength);
Example:
var passwordEntry = "StackOverflow";
var saltEntry = "SaltyMcSalty";
var keyBytes = new byte[32 + 1];
Array.Clear(keyBytes, 0, keyBytes.Length);
var result = CCKeyCerivationPBKDF(2, passwordEntry, passwordEntry.Length, saltEntry, saltEntry.Length, 3, 1, keyBytes, keyBytes.Length);
Use "native" objects / reduced marshaling:
(Had to due it this way to get passed on a military/aerospace certification/review)
[DllImport(ObjCRuntime.Constants.libSystemLibrary, EntryPoint = "CCKeyDerivationPBKDF")]
public extern static int CCKeyCerivationPBKDF(
int algorithm,
IntPtr password,
nuint passwordLen,
IntPtr salt,
nuint saltLen,
UInt32 prf,
nuint rounds,
IntPtr derivedKey,
nuint derivedKeyLength);
Example (w/ Base64):
var passwordEntry = "StackOverflow";
var passwordBytes = System.Text.Encoding.UTF8.GetBytes(passwordEntry);
var passwordBase64 = Convert.ToBase64String(passwordBytes);
var passwordNSStringBase64 = new NSString(passwordBase64);
var passwordNSData = new NSData(passwordNSStringBase64, NSDataBase64DecodingOptions.None);
var saltEntry = "SaltyMcSalty";
var saltBytes = System.Text.Encoding.UTF8.GetBytes(saltEntry);
var saltBase64 = Convert.ToBase64String(saltBytes);
var saltNSStringBase64 = new NSString(saltBase64);
var saltNSData = new NSData(saltNSStringBase64, NSDataBase64DecodingOptions.None);
var keyBytes = new NSMutableData();
keyBytes.Length = 33;
var result = CCKeyCerivationPBKDF(2, passwordNSData.Bytes, passwordNSData.Length, saltNSData.Bytes, saltNSData.Length, 3, 1, keyBytes.MutableBytes, keyBytes.Length - 1);