I want to send an out of band message (don't worry about how it gets there) to a program I've written on a distant machine. I want the program to have some confidence the message is legit by attaching a digital signature to the message. The message will be small less than 200 characters.
It seems a public key based signature is what I want to use. I could embed the public key in the program.
I understand that the program would be vulnerable to attack by anyone who modifies it BUT I'm not too worried about that. The consequences are not dire.
I've looked through the MSDN and around the web but the prospect of diving in is daunting. I'm writing in straight c++, no NET framework or other fancy stuff. I've had no experience including NET framework stuff and little luck during previous attempts.
Can anyone point me at some very basic resources to get me started?
I want to know
How to generate the public and private keys
How to sign the message
How to verify the signature
You could try looking at the Keyczar library. It provides a high level abstraction to cryptographic functions with the aim to make is easy for developers to do crypto correctly. As an added bonus it has c++ bindings.
There is also Cryptlib which has been around for a while, and NaCl. As with Keyczar these libraries aim to provide a high level abstraction for common crypto functions.
gpgme is a high-level cryptographic API for GnuPG, written in C, but with bindings for a number of languages. GnuPG has excellent docs and is easy to use, so you can play around 'manually' on the command line and get a feel for how the key operations work, then look up the functions you need for your code in the API.
Related
I need to implement an authentication procedure between a reader an NFC tag but being my knowledge limited in this area I will appreciated some aid in order to understand few concepts.
Pardon in advance for rewrite the Bible but I could not summarize it more.
There are many tags families ( ICODE, MIFARE, NTAG...) but after doing a research I think NTAG 424 DNA matches my requirements(I need mainly authentication features).
It comes with AES encryption, CMAC protocol and 3-pass-authentication system and here is when I started to need assistance.
AES -> As I am concerned this is a block cipher to encrypt plain texts via permutations and mapping. Is a symmetric standard and it does not use the master key, instead session keys are used being them derivations from the master key. (Q01: What I do not know is where this keys are stored in the tag. Keys must be stored on specialized HW but no tag "specs" remark this, apart from MIFARE SAM labels.)
CMAC -> It is an alteration of CBC-MAC to make authentication secure for dynamically sized messages. If data is not confidential then MAC can be used on plain-texts to verify them, but to gain confidentiality and authentication features "Encrypt-than-mac" must be pursuit. Here also session keys are used, but not the same keys used in the encryption step.(Q02: The overall view of CMAC may be a protocol to implement verification along with confidentiality, this is my opinion and could be wrong.)
3-pass-protocol -> ISO/IEC 9798-2 norm where tag and reader are mutually verified. It may also use MAC along with session keys to achieve this task.(Q03: I think this is the upper layer of all the system to verify tags and readers. The "3 pass protocol" relays in MAC to be functional and, if confidentiality features are also needed, then CMAC might be used instead of single MAC. CMAC needs AES to be functional, applying session keys on each step. Please correct me if I am posting savages mistakes)
/*********/
P.S: I am aware that this is a coding related forum but surely I can find here someone with more knowledge than me about cryptography to answer this questions.
P.S.S: I totally do not know where master and session keys are kept in the Tag side. Have they need to be include by a separate HW along with the main NFC circuit ?
(Target)
This is to implement a mutual verification process between tag and reader, using the NTAG 424 DNA TagTamper label. (The target is to avoid 3ยบ parties copies, being authentication the predominant part instead of message confidentiality)
Lack of knowledge of cryptography and trying to understand how AES, CMAC and the mutual authentication are used on this NTAG.
(Extra Info)
NTAG 424 DNA TT: https://www.nxp.com/products/identification-security/rfid/nfc-hf/ntag/ntag-for-tags-labels/ntag-424-dna-424-dna-tagtamper-advanced-security-and-privacy-for-trusted-iot-applications:NTAG424DNA
ISO 9798-2: http://bcc.portal.gov.bd/sites/default/files/files/bcc.portal.gov.bd/page/adeaf3e5_cc55_4222_8767_f26bcaec3f70/ISO_IEC_9798-2.pdf
3-pass-authentication:https://prezi.com/p/rk6rhd03jjo5/3-pass-mutual-authentication/
Keys storage HW:https://www.microchip.com/design-centers/security-ics/cryptoauthentication
The NTAG424 chips are not particularly easy to use, but they offer some nice features which can be used for different security applications. However one important thing to note, is that although it heavily relies on encryption, from an implementation side, that is not the main challenge, because all of the aes encryption, cmac computation and so on is already available as some sort of package or library in most programming languages. Some examples are even given by nxp in their application note. For example in python you will be able to use the AES package from Crypto.Cipher import AES as stated in one of the examples of the application note.
My advice is to simply retrace their personalization example beginning at the initial authentication, and then work your way up to whatever you are trying to achieve. It is also possible to use these examples in order to test the encryption and the building of apdu commands. Most of the work is not hard, but sometimes the NXP documents can be a bit confusing.
One small note, if you are working with python, there is some code available on github which you might be able to reuse.
For iOS, I'm working on a library for DNA communication, NfcDnaKit:
https://github.com/johnnyb/nfc-dna-kit
I recently read about decompilation of iOS apps and I'm now really concerned about it. As stated in the following posts (#1 and #2) it is possible to decompile an iOS which is distributed to the App Store. This can be done with jailbreak and I think with copying the app from memory to hdd. With some tools it is possible to
read out strings (strings tools)
dump the header files
reverse engineer to assembly code
It seems NOT to be possible to reverse engineer to Cocoa code.
As security is a feature of the software I create, I want to prevent bad users from reconstructing my security functions (encryption with key or log in to websites). So I came up with the following questions:
Can someone reconstruct my saving and encryption or login methods with assembly? I mean can he understand what exactly is going on (what is saved to which path at which time, which key is used etc., with what credentials is a login to which website performed)? I have no assembly understanding it looks like the matrix for me...
How can I securly use NSStrings which cannot be read out with strings or read in assembly? I know one can do obfuscation of strings - but this is still not secure, isn't it?
This is a problem that people have been chasing for years, and any sufficiently-motivated person with skills will be able to find ways to find out whatever information you don't want them to find out, if that information is ever stored on a device.
Without jailbreaking, it's possible to disassemble apps by using the purchased or downloaded binary. This is static inspection and is facilitated with standard disassembly tools. Although you need to have a tool which is good enough to add symbols from the linker and understand method calls sufficiently to be able to tease out what's going on. If you want to get a feel for how this works, check out hopper, it's a really good disassembly/reverse-engineering tool.
Specifically to your secure log in question, you have a bigger problem if you have a motivated attacker: system-based man-in-the-middle attacks. In this case, the attacker can shim out the networking code used by your system and see anything which is sent via standard networking. Therefore, you can't depend on being able to send any form of unencrypted data into a "secure" pipe at the OS or library level and expect it not to be seen. At a minimum you'll need to encrypt before getting the data into the pipe (i.e. you can't depend on sending any plain text to standard SSL libraries). You can compile your own set of SSL libraries and link them directly in to your App, which means you don't get any system performance and security enhancements over time, but you can manually upgrade your SSL libraries as necessary. You could also create your own encryption, but that's fraught with potential issues, since motivated hackers might find it easier to attack your wire protocol at that point (publicly-tested protocols like SSL are usually more secure than what you can throw together yourself, unless you are a particularly gifted developer with years of security/encryption experience).
However, all of this assumes that your attacker is sufficiently motivated. If you remove the low-hanging fruit, you may be able to prevent a casual hacker from making a simple attempt at figuring out your system. Some things to avoid:
storing plain-text encryption keys for either side of the encryption
storing keys in specifically named resources (a file named serverkey.text or a key stored in a plist with a name which contains key are both classics)
avoid simple passwords wherever possible
But, most important is creating systems where the keys (if any) stored in the application themselves are useless without information the user has to enter themselves (directly, or indirectly through systems such as OAUTH). The server should not trust the client for any important operation without having had some interaction with a user who can be trusted.
Apple's Keychain provides a good place to store authentication tokens, such as the ones retrieved during an OAUTH sequence. The API is a bit hard to work with, but the system is solid.
In the end, the problem is that no matter what you do, you're just upping the ante on the amount of work that it takes to defeat your measures. The attacker gets to control all of the important parts of the equation, so they will eventually defeat anything on the device. You are going to need to decide how much effort to put into securing the client, vs securing the server and monitoring for abuse. Since the attacker holds all of the cards on the device, your better approach is going to be methods that can be implemented on the server to enhance your goals.
Can I encrypt a Visual Basic project so it can't be decompiled by dotPeek or any other software? I have done some research and I can't find anything.
The question you have asked is an excellent example of The XY Problem, where you have problem X, come up with solution Y, and then ask how to perform or implement Y. I shall answer Y first and advise you on X, which is what you really should have asked, e.g. "If I have an API key in my source code, how can I keep it safe?".
The answer to Y is kind-of yes. You can obfuscate your .NET assemblies in such a way that it becomes moderately difficult to determine exactly what the source code does. However, constant values, such as your API key, will be significantly easier to retrieve since it is a constant string value. The important thing to remember here is that obfuscation is not security, the API key most definitely can still be retrieved.
The answer to X (the question you should have asked), and the advice that you should follow, is to not store the API key in your application at all. Have an external server that you can send requests to that will in turn use the API key to retrieve relevant data and perform operations. Having your own server as a middle-man means that you can ratelimit requests and authenticate users yourself if you choose to. API keys should never be stored in client-side code (unless you have things like public and private API keys, which I believe Stripe, among others, use).
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I have researched on each element or system that I am willing to implement into a generic software licensing system for my soon-to-be apps (irrelevant, as this should work, or be usable on all of my applications).
I have created a DLL with my licensing class in it.
It is as follows:
(1)
I have applied the InternalsVisibleTo() attribute main class (with child classes), which makes all of the internal classes, and their methods, which are declared Friend, visible to external assemblies with the sepcified PublicKey.
I have made the reference to the app name, and it's PublicKey. (Both the licensing, and the external assembly, are signed with the same key (.snk file)
(2)
All (where possible) members, properties etc. are delcared Friend or Private or just Dim...ed .
(3)
My licensing class has a String variable; declared:
Private Shared _Key As String = "H58N2-00V93"
This variable is the special password, if you will, of my DLL, and is required to access the methods in my DLL.
There is also a Public String variable (let's call it "AccessKey"), which should be initialized with the main class, like so:
Dim licDLL As New LicensingAssemblyName.LicensingMainClass With {.AccessKey="H58N2-00V93"}
(4)
Then, I have a Function (let's call it "CheckKey"), which checks whether the Public, initialized variable ("AccessKey" is equal to the pre-defined, Friend key ("_Key"), whereupon an exception will be thrown, if they are not equal - preventing method from continued/used.
(5)
At each first line of every Sub, Function etc., I have inserted a call to this function.
These are just the 'security' measures I've taken to prevent external assemblies from using my DLL in another app, to perhaps exploit the system or generate keys.
Now for the licensing measures.
(1)
I have a key generator (very basic), which generates codes upon a given format (Like: "#-$" for a number, a dash, followed by a letter.)
I have included an encryption class in this program, which uses Rijndaenal, and applies salt.
I have set the key generator to encrypt each separate key upon generation, then append it to a new line of a file, which we'll call "my_licenses.txt".
I use the same password for each one (obviously). It is quite long, and includes many different characters (if that makes ANY difference). I considered this to be a secure way since I didn't think ANYONE could decrypt a string without the password, until I was told by another programmer, who advised against using plain text encryption as a method to secure these keys. Please help me with this.
(2)
In my licensing DLL, I have a declaration:
Friend Shared Function IsKeyValid(ByVal KeyDB As String, ByVal Key As String) As Boolean
This function decrypts each key in the file (the specified database, using the same pass code used when encrypting them in the key generation program).
Then I do a For Each, Next loop to, determining whether the specified "Key" value equals any in the key 'database', "my_licenses.txt". But here's the catch.
I have an Function which returns a unique code for the computer it's running on (using hardware IDs etc.). This Function helps me protect against the use of the same key on multiple computers (unless I implement a system for allowing this, limited times) and is required as the last 5 characters of the "Key".
After checking, this Function returns a value of the result (True or False).
Finally (phew), each assembly (the licensing one, and any external ones which utilize it) are obfuscated -and likewise signed (all assemblies, with the same key (.snk) file)- by CodePlex's Confuser (A free, and highly recommended obfuscator for .NET).
I hope this hasn't been too long/not detailed enough/difficult to understand. (If so, tell me what you don't understand).
This is my first post/question of any kind, so be nice. Also thank you for reading.
I hope you can help.
And just to confirm, my question is this: Would this system be secure enough to protect against the average hacker?
P.S. I am only a beginner, so answers for a beginner would be especially appreciated ;)
*UPDATE: I have actually reduced the length of this question, and improved its understandability (believe it or not). So this is the best I can do.
That's an insane wall of text so you kind of lost me. And, to be honest I stopped reading seriously when I saw you had a hardcoded key inside the binary that you plan to distribute... But there are two questions you ought to ask yourself:
Is your application likely to be so successful that there is sufficient demand for it so that people with the appropriate skillset will be inclined to reverse it and release a keygen and/or pirated version?
And wouldn't your time be better spent adding cool features to the application instead of licensing code which does nothing to improve the application itself?
Don't get me wrong. I'm all for people getting paid for their work and I don't object to people licensing their software; as a matter of fact, one of the projects I worked on was a custom licensing engine which was tracking a little over 100,000 licenses last I checked. But make sure that if you decide to implement licensing that the effort you put into it doesn't exceed the effort you put into the actual software you're licensing.
With all that said, here's what I would do:
Generate a lot of licensing keys (using whatever format you want)
Hash those keys using something like SHA-256 or SHA-512.
Create an array (using whatever syntax is appropriate to your language of choice) that contains the key hashes.
Include the array inside your application.
With that setup, to verify a license, all you need to do is:
Hash the input using the same algorithm as before.
Iterate the array, comparing it with the result of the hash. If they match, the key is licensed. If they don't, continue.
If you get to the end of the table the key is not licensed.
Do not immediately exit the application if the key isn't licensed. Instead set a flag that prevents the use of important commands (e.g. "Save") or set a timer for 60 seconds plus a random number of to exit the application.
Compile and then digitally sign your application with Authenticode. Have the application itself validate the signature to try and discourage casual tampering.
If you are so inclined, you could even encrypt the hashes, although that is unlikely to help against the sort of attack that someone would mount against this scheme.
To be clear: this is not bulletproof (then again, no licensing mechanism is) and it's possible for someone sufficiently skilled to break it in a number of ways. But it's almost certainly going to be more than good enough for your project.
Security doesn't have an absolute value, it has to be measured against the payoff. If your app is holding some nuclear codes I'd say go pay a specialized consultant for this. If you're storing grandma's secret recipes - you're good to go.
I read the whole post and it's still not clear what's the purpose of the hard-coded key or how do you manage the individual encryption keys for each license: encryption is not just about how strong an algorithm you use or how long your password is; it's also about how do you hide your passwords, how do you transmit them, what do you do in edge cases (interrupted connection, failed decryption etc) and many other things.
From the looks of it I'd say you're in the "good to go" category only because your app doesn't sound like a high-profile target to crack and you mostly want to deter the casual cracking attempt from a frustrated developer who doesn't like your licensing scheme (: and the obfuscation alone would deter most when it comes to reverse-engineering your code. I'm not familiar with your code to tell if there's any other, easier ways to bypass licensing, such as the popular method of copying the licensing file itself if it's not tied to the machine or user profile...
There are many workarounds online, but only hashing system described here or something based on public key cryptography can be secure enough to serve licensing.
I personally prefer and use commercial product: http://www.treekslicensinglibrary.com - Treek's Licensing Library. It's cheap, easy to setup and really secure as it uses previously meant public key cryptography to work with license.
Edit: To compare with hashes of serial numbers - this solution does not require to predefine accepted serial numbers. 1000 hashes in apps = 1000 licenses, for more you need to update your app. Public key cryptography based license systems do not have this disadvantage.
You can use a .NET Obfuscate application to secure it. All .NET application may decompile with .NET Reflector, so search in your browser the application to obfuscate .net application. This will work as i know, everyone that want to decompile your application will prevent by the obfuscate
I am trying to encrypt an NSString to both NSString and NSData in Objective-C and so I began a search.
I started off here, but that went way over my head, unfortunately.
I then found myself at this post and it came across to be very easy to follow, so I went along and tried to figure out the implementation. After looking over the implementation, I saw the second answer in the post and saw he had more adaptable implementations, which brought me to his gist. As per the gist readme, he "took down this Gist due to concerns about the security of the encryption/decryption". That leads me to believe that the security of the implementation from above has security flaws as well.
From that gist, however, he mentioned another alternative that I could use for encryption. After taking a look at the code, I noticed that it generates NSData with "a header, encryption salt, HMAC salt, IV, ciphertext, and HMAC". I know how to handle that to decode using the same library again, but how would I pass this off to a server guy, given that I don't quite know what I'm sending to him?
At the root of it all, I'm in over my head. Given what I said above and knowing that I don't have the time to take on a lot of learning for this, unless if it is absolutely necessary, how should I best handle going about this encoding/decoding process, given a private key with the end goal of shipping it off to a server that is not designed by me? (How's that for a run on sentence!)
Maybe you should ask the server guy? When ever you have encryption between too parties you have to have some kind of agreement on the format of that data, the raw primitives don't handle that alone, not to mention it's easy to mess things up security wise dealing with just the primitives and the desire to just send the aes ciphertext alone is going to cause mistakes.
RNCryptor, which you mention, is a high level encryption library it defines a simple format that others would have to conform too, it's simple thus helps going cross platform, but it has that extra that you need to do AES properly. There are other libraries like that too (NaCL, GPGME, and Keyczar), that are not as simple in format, but simple in usage, so you'd need to be able to use the library on both ends, but I'd highly recommend that you uses something like that, if you can, rather than rolling your own.
Keyczar specifically exists for java, python, c++, c# and go, so if you can use the c++ version on the iOS (or Mac, which ever you are targeting on the client) you might be good on the server as there are several choices.