CDF – Crypto Differential Fuzzing

CDF - Crypto Differential Fuzzing

CDF is a software to robotically take a look at the correctness and safety of cryptographic software program. CDF can detect implementation errors, compliance failures, aspect-channel leaks, and so forth.

CDF implements a mixture of unit exams with “differential fuzzing”, an strategy that compares the conduct of various implementations of the identical primitives when fed edge instances and values maximizing the code protection.

Unlike normal-goal fuzzers and testing software program, CDF is:
  • Smart: CDF is aware of what sort of algorithm it is testing and adapts to the examined features

  • Fast: CDF exams solely what must be examined and parallelizes its exams as a lot as attainable

  • Polyvalent: CDF is not particular to any language or API, however helps arbitrary executable packages or scripts

  • Portable: CDF will run on any Unix or Windows platform, since it’s written in Go with none platform-particular dependency

The goal of CDF is to supply extra environment friendly testing software to builders and safety researchers, being simpler than take a look at vectors and cheaper than handbook audit of formal verification.

CDF was first offered at Black Hat USA 2017. You can view the slides of our presentation, which comprise normal details about the rationale behind and the design of CDF.

CDF is coded in
Go, the present model has been developed utilizing Go 1.8. It has no dependencies outdoors of Go’s standard library.
However, we offer instance packages to be examined utilizing CDF, that are in C, Python, C++, Java and Go and require particular crypto libraries to be run. Currently required libraries are:

make will construct the cdf binary.
A bunch of instance packages can be found beneath example: make examples-all will construct all of the examples, whereas make examples-go will solely construct the Go examples.
make take a look at will run unit exams (of CDF).

For starters you could wish to view utilization information by working cdf -h.
You could then strive an instance such because the rsaenc interface in opposition to the RSA OAEP Go and CryptoPP examples. Viewing CryptoPP as our reference, you possibly can take a look at the Go implementation by doing:

cdf rsaenc /examples/oaep_rsa2048_go /examples/oaep_rsa2048_cryptopp

This command will carry out varied exams particular to the rsaenc interface.
In this instance, CDF ought to complain concerning the most public exponent measurement the Go implementation help: if we verify its code we will see the general public exponent is being saved as a traditional integer, whereas in CryptoPP (and most different implementations), it’s saved as a giant integer. This is nonetheless by design and can possible not be modified.
Parameters are outlined in config.json. Most parameters are self-explanatory. You could wish to set others personal keys for rsaenc and ecdsa (these interfaces are examined with fastened keys, though some key parameters, such because the exponents, are modified in a number of the exams).
The seed parameter allows you to change the seed utilized in CDF’s pseudo-random turbines. (Yet, the examined program could also be utilizing some PRNG seeded in any other case, just like the OAEP examples.) The concurrency parameter allows you to set the variety of concurrent goroutine CDF must be spawning when forking the packages. Note that it’s best to maintain this quantity under the actual variety of cores. The verboseLog parameter, if set to true, will write all packages’ inputs and outputs, even for the succesful exams, to a file log.txt.

In order to check your software program utilizing CDF, it’s important to create a program that reads enter and writes output in conformance with CDF interfaces, and that internally calls the examined program. CDF interfaces are abstractions of a crypto performance, with a view to permit black-field testing of arbitrary implementations.
For instance, when you applied the ECDSA signature scheme, your program ought to satisfies the ecdsa interface and as such take as inputs four or 5 arguments, respectively with a view to signal a message or confirm a signature. These arguments are the general public X coordinate, the general public Y coordinate, the personal D large integer and the message you wish to signal after which it ought to output solely the massive integers R and S every on a newline. Or, to confirm a message, it ought to settle for X,Y, the R, the S and the message after which it ought to solely output True or False. The interfaces’ specs are detailled below.
Our examples of interface implementations will assist you create your owns.
Error dealing with is left to the examined program, nonetheless to have significant errors in CDF it’s best to exit on failure, return a error code and print an error message.
The interface program might be written in any language, it simply must be an executable file conformant with a CDF interface. An interface program is usually written in the identical language because the examined program, however that is not obligatory (it might be a wrapper in one other language, for instance for Java packages).
CDF at present helps the next interfaces, whereby parameters are encoded as hexadecimal ASCII strings, except described in any other case:

The dsa interface exams implementations of the Digital Signature Algorithm (DSA). It should help the signature and verification operations:

Operation Input Output
Signature p q g y x m r s
Verification p q g y r s m reality worth

Here p, q, g are DSA parameters, y is a public key, x is a personal key, m is a message, r and s kind the signature, which should returned separated by a newline. The reality worth, both “true” or “false”, is represented as a string.
The dsa interface helps an elective take a look at: the-h permits to bypass the hashing course of and straight present the hash worth to be signed. This permits CDF to carry out extra exams, akin to checking for overflows or hash truncation.

The ecdsa interface exams implementations of the Elliptic Curve Digital Signature Algorithm (ECDSA). It should help the signature and verification operations:

Operation Input Output
Signature x y d m r s
Verification x y r s m reality worth

Here x and y are a public ECDSA key coordinates, d is a personal key, m is a message, and r and s kind the signature, which have to be returned separated by a newline. The reality worth, both “true” or “false”, is represented by a string.
The flag -h serves the identical goal as with dsa.
Please observe that our present design assumes a set curve, outlined within the examined program.
To acquire reproducible outcomes with these exams and leverage all of CDF detection’s skills, it’s important to both seed you random generator with a set seed or use a deterministic ECDSA variant, in any other case CDF cannot detect issues akin to similar tags points robotically.

The enc interface exams symmetric encryption and decryption operations, sometimes when carried out with a block cipher (stream ciphers might be examined with the prf interface). It should help encryption and decryption:

Operation Input Output
Encryption ok m c
Decryption ok c r

Here ok is a key, m is a message, c is a ciphertext c and r is a recovered plaintext.

The prf interface exams keyed hashing (pseudorandom features, MACs), in addition to stream ciphers:

Operation Input Output
Computation ok m h

Here ok is a key, m is a message (or nonce in case of a stream cipher), and h is the results of the PRF computation. Our interface assumes fastened key measurement and variable enter lengths. If a particular secret’s to be specified, it’s the accountability of the examined program to disregard the important thing enter or the xof interface could also be a more sensible choice.

The rsaenc exams RSA encryption and decryption, each OAEP (PKCS 2.1) and PKCS 1.5:

Operation Input Output
Encryption n e m c
Decryption p q e d c r

Here n is a modulus, e is a public exponent (for compatibility with sure libraries, e can also be wanted for decryption), m is a message m, p and q are n’s issue (such that p > q, since libraries generally require it), d is a personal exponent, and r is a recovered plaintext.

The xof interface exams hash features, extendable-output features (XOFs), deterministic random bit turbines (DRBGs):

Operation Input Output
Computation m h

Here m is the message and h is the outcome h.

CDF is predicated on preliminary concepts by JP Aumasson, first disclosed at WarCon 2016, and many of the code was written by Yolan Romailler.


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