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    Lei Zhang
    @lei-april
    Hi, there's another active project on ZKP DSL called 'Zinc': https://github.com/matter-labs/zinc. I think it has quite similar functionalities to ZoKrates. Do you guys have any insight on how Zinc and ZoKrates compare?
    smithsen
    @smithsen

    Hi, Sorry for the previous issues I had written down, I was able to sort them out. I am trying to work with the example in https://zokrates.github.io/sha256example.html#computing-a-hash-using-zokrates and when I execute the first line of code "./zokrates compile -i hashexample.zok" I get an error that "Compiling hashexample.zok

    Compilation failed:

    hashexample.zok:1:1
    I/O Error: No file found at hashes/sha256/512bitPacked
    " What could be the possible way to fix this problem? Note I am using the installation from source because I want to compare groth and pinochio

    smithsen
    @smithsen
    Update, I tried looking around, so I found sha512bitPacked.zok in hashes/sha256 and I tried doing doing instead of "import "hashes/sha256/512bitPacked" as sha256packed" to do "import "hashes/sha256/512bitPacked.zok" as sha256packed
    " I tried using the fix mentioned in "https://ethereum.stackexchange.com/questions/67011/in-tutorial-of-ethereum-zokrates-high-level-code-compile-error" But still seems to give the same error. What can be the possible fix ?
    smithsen
    @smithsen
    I actually fixed the problem for now. First I used the single line command to install .zokrates and specified the path and then I also did the installation from the source. When I need pinochio I am using the source installation and for all other compilation I am using "zokrates ....". Hope this is the fix. If there is any other solution which does not require me to use the one line installation and directly do everything from source installation please do let me know
    hou
    @turfT
    hi, I review ethsnark's verifier.sol and zokrate's verifier.sol. It seems that zokrates' compile a lot BN128 code in solidity. any suggestion or document for this design?
    e.g. function pairingProd4 ..
    hou
    @turfT
    zokrates also use precompile (namely EIP1108) assembly. So I am quite confused about other field operations written in solidity.
    Thibaut Schaeffer
    @Schaeff
    Hi @turfT, the delta probably comes from the fact that we implemented proving schemes which require G2 operations that are not offered by the precompiles
    Thibaut Schaeffer
    @Schaeff
    https://eprint.iacr.org/2017/540.pdf 5.4 in this paper, the first verification equation is 4 pairing operations, and the left hand side requires addition on G2
    hou
    @turfT
    great, thx a lot @Schaeff
    Mohsen Rahnamaei
    @mohsen158
    hi, I am testing hello world of Zokrate but always I get true, even in wrong proof. does anybody know where am I wrong?
    Darko Macesic
    @dark64

    You might be confusing the program returning 0/1 and the proof being invalid/valid. Proofs generated by ZoKrates are always valid (the verifier returns always true), you'd need to fiddle with the proof yourself to make it invalid.

    @mohsen158

    Neo
    @creepteks
    Hi, there. I am a little bit confused regarding the ability to prove knowledge of an arbitrary preimage for a hashed value. All examples I have seen so far are covering the fact that the preimage is hardcoded in the .zok file. Am I correct?
    Thibaut Schaeffer
    @Schaeff
    @Mahdad-Baghani do you mean the hash is hardcoded?
    Neo
    @creepteks
    @Schaeff
    Yeah, I think I'm still a little bit confused. Take this for an example: https://blog.decentriq.ch/proving-hash-pre-image-zksnarks-zokrates/
    I think I was looking at some elementary examples which kinda gave me the idea that it is only possible to hardcode the hash digest into zokrates and then create the circuit.
    I actually wanted to understand zkDAI better: https://medium.com/@atvanguard/zkdai-private-dai-transactions-on-ethereum-using-zk-snarks-9e3ef4676e22
    I was inspecting the zk-circut at https://github.com/atvanguard/ethsingapore-zk-dai/blob/master/ethereum/zk-circuit.code, and then I figured that I was probably misguided as this next example shows that you can create a circuit using zokrates to prove/verify knowledge of preimage of arbitrary hashes (with limitations regarding the compile-time determination of size of the hashes, of course). Am I right?
    import "LIBSNARK/sha256packed"
    
    // https://zokrates.github.io/sha256example.html#computing-a-hash-using-zokrates
    // A field value can only hold 254 bits due to the size of the underlying prime field used by zokrates. Therefore, 256 bit values need to be passed as 2 params of 128 bit values.
    
    // https://zokrates.github.io/concepts/stdlib.html?highlight=sha256#sha256packed
    // At the time of writing sha256packed takes 4 field elements as inputs, unpacks each of them to 128 bits (big endian), concatenates them and applies sha256. It then returns two field elements, each representing 128 bits of the result.
    
    // Public inputs
    // onh0 + onh1: Hash of the note (secret note)
    // nn1h0 + nn1h1: Hash of the new note 1
    // nn2h0 + nn1h1: Hash of the new note 2
    
    // Private inputs
    // ona + onb: secret key of the sender
    // onc + ond: (256 bits) representing the value of the note to be spent
    
    // nn1a + nn1b: public key of the receiver
    // nn1c + nn1d: the value of the note to be sent
    
    // nn2c + nn2d: leftover change
    def main(field onh0, field onh1, private field ona, private field onb, private field onc, private field ond, field nn1h0, field nn1h1, private field nn1a, private field nn1b, private field nn1c, private field nn1d, field nn2h0, field nn2h1, private field nn2c, private field nn2d) -> (field):
        // get public key corresponding to private key
        // too complex to implement for the hackathon :p - so sending in the public key instead
        field pka = ona
        field pkb = onb
    
        // old note
        h0, h1 = sha256packed(pka, pkb, onc, ond)
        h0 == onh0 // verify with public input (hash of the note)
        h1 == onh1
    
        // new note 1 that goes to pkreciever
        h0, h1 = sha256packed(nn1a, nn1b, nn1c, nn1d)
        h0 == nn1h0
        h1 == nn1h1
    
        // new note (left over change) that goes back to sender (pk)
        h0, h1 = sha256packed(pka, pkb, nn2c, nn2d)
        h0 == nn2h0
        h1 == nn2h1
    
        ond == nn1d + nn2d // assuming the values fit in 128 bit nums - hence onc, nn1c, nn2c are 0
        return 1
    Thibaut Schaeffer
    @Schaeff
    @Mahdad-Baghani so let me make it clear here: it's absolutely possible to pass the hash as a parameter, typically a public one so that the verifier can see it. The cost for that is a slightly bigger proof and slightly more expensive verification, as is the case with any public input.
    Neo
    @creepteks
    @Schaeff thanks for the clarification
    hou
    @turfT
    Hi, can I use zokrates as a tool for generating circuits for default backend bellman? I wish I could only use Zokrates as a DSL to programming circuit and reuse it in bellman. Any suggestions?
    Thibaut Schaeffer
    @Schaeff
    @turfT Hey, what do you want to do in bellman with the zokrates circuit that you can't do with zokrates itself? Have a zokrates circuit inside a bellman circuit?
    hou
    @turfT
    Transfer a zokrates circuit into bellman circuit. I tried to write some zokrates circuit like a Poseidon hash version payment zk protocol, it works pretty well. So I wonder can I transfer circuits into bellman version, only for learning purposes..
    thx for your kind relay @Schaeff
    reply ..
    smithsen
    @smithsen
    Hey everyone. I was wondering if I can take hash of a matrix (I need this to make a circuit) and what would be the right way in case I want to use sha256?
    Thibaut Schaeffer
    @Schaeff
    @smithsen inside the program, you could iterate through the matrix filling an array that you then hash?
    @turfT Under the hood, zokrates creates a bellman circuit so that it can then use the bellman backend
    here https://github.com/Zokrates/ZoKrates/blob/master/zokrates_core/src/proof_system/bellman/mod.rs#L195 the Computation struct (which can be created from a compiled zokrates program and witness) implements the Circuit trait from bellman, so conceptually it could be used as part of a bigger bellman circuit, if that's what you're intending to do
    Tim
    @timhc22
    Hello, had a chat with the team on twitter (@timhc22) what's the best way to chat?
    15 replies
    smithsen
    @smithsen

    @smithsen inside the program, you could iterate through the matrix filling an array that you then hash?

    Alright, I will try with that

    Tim
    @timhc22
    Hey, would I be right in thinking that zokratesProvider.compile("def main(private field a) -> (field): return a * a") is compiling down to web assembly?
    sorry if thats a pretty basic question, I'm pretty new to this
    smithsen
    @smithsen
    Hi, I am sorry but I was reading an article "https://medium.com/zokrates/building-identity-linked-zksnarks-with-zokrates-a36085cdd40" and I was not very clear with what proofOfOwnership.code does exactly in the second piece of code?
    Tim
    @timhc22
    looks like babyjubjubparams.code is the 'pre image', and proofOfOwnership is just generating a non-repudiated (if that is the correct term) hash (proof), the other two inputs/parameters being Alice's public and private key right?
    like I said, I'm pretty new to this, so may be wrong, but thanks for sharing that, it was a super interesting read!
    Tim
    @timhc22
    ah no, babyjubjub is this https://github.com/barryWhiteHat/baby_jubjub_ecc, ignore me
    smithsen
    @smithsen

    looks like babyjubjubparams.code is the 'pre image', and proofOfOwnership is just generating a non-repudiated (if that is the correct term) hash (proof), the other two inputs/parameters being Alice's public and private key right?

    Hey, I think the same too but I am essentially generating a matrix in another code and then I want to put it in the hash generation system and then use the proof as such, the only problem is my matrix dimension is like 128 x 128 and converting to an array and then doing hash is kinda scary. I was wondering if there are some direct tools.

    Thibaut Schaeffer
    @Schaeff
    @smithsen proofOfOwnership takes a public key and a private key, and makes sure that the public key is derived from the private key. If you make the private key a private input to the program, you're essentially proving that you know the private key to a given public key.
    smithsen
    @smithsen
    Ok so it is like a preliminary stage checking that yes indeed we have the data. So as given in the example there in https://medium.com/zokrates/building-identity-linked-zksnarks-with-zokrates-a36085cdd40 , the author says that Alice wants to prove her age, if I have to consider the picture of Alice's ID card and then work on that, my idea was converting it in matrix and then putting it as a private key in the code written in the blogpost, it is seems too much. Is there a way in Zokrates that I can take the image in ?
    Darko Macesic
    @dark64

    Hey, would I be right in thinking that zokratesProvider.compile("def main(private field a) -> (field): return a * a") is compiling down to web assembly?

    no, zokrates itself is compiled down to web assembly which the javascript library calls to compile your program, this makes it possible for zokrates to be run in browser/node environments

    smithsen
    @smithsen

    Ok so it is like a preliminary stage checking that yes indeed we have the data. So as given in the example there in https://medium.com/zokrates/building-identity-linked-zksnarks-with-zokrates-a36085cdd40 , the author says that Alice wants to prove her age, if I have to consider the picture of Alice's ID card and then work on that, my idea was converting it in matrix and then putting it as a private key in the code written in the blogpost, it is seems too much. Is there a way in Zokrates that I can take the image in ?

    Can someone please help me with this one? Or at least if can give the reference as in where to look for that would be great. Thanks

    DobPP
    @dobpp
    Hi
    DobPP
    @dobpp
    I'd like to create zokrates generating serial numbers, is it possible?
    Thibaut Schaeffer
    @Schaeff
    @smithsen how do you make sure that Alice doesn't photoshop the ID?
    Thibaut Schaeffer
    @Schaeff
    @smithsen One approach for these kinds of situations (say, proving that Alice is over 18) is to have a reputable entity sign Alice's birth date and public key and give the signature to Alice, then Alice inputs her birth date and the signature as private inputs, and her public key and the reputable entity's public key as public inputs, basically saying: "I know a signature by this reputable entity which claims that I was born on date d with d more than 18 years ago". Note that the reputable entity signed the birth date and not the statement "Alice is over 18", so that Alice can reuse this signature to prove whatever she needs to
    smithsen
    @smithsen

    @smithsen how do you make sure that Alice doesn't photoshop the ID?

    I mean Alice can but possibly a reputable entity can hash the image right, as signature ?

    Thibaut Schaeffer
    @Schaeff
    In theory yes, however doing image processing inside a snark is much much more expensive than verifying a digital signature.
    smithsen
    @smithsen
    I see, ok I wanted to process an image inside the snark
    stevewu
    @Stevewu1234
    Hi, I'm learning zk-snark used in Ethereum. And I'm confused with the authenticity of one data: using groth16 algorithm to generate zk-snark proof and the estimation is 1 tx(200bytes) 50MB. Can I use ZoKrates to prove data authenticity? Or have I made a misunderstanding?
    Tim
    @timhc22
    Hello, for anyone who has worked with the zokrates.js library:
    I have managed to get it working with a react app locally, but when I host it (on AWS S3), I'm getting an error with Mime types (HERE: https://web3.unegma.com/page-three and HERE: https://github.com/timhc22/zokrates/blob/main/client/src/pages/PageThree/PageThree.js), I've tried to figure out how to add the mime type on s3, but it isn't specific to one file. Any idea if I will need to make the calculations using zokrates.js on a server, and do an api call from the frontend instead, or is there some kind of workaround? Thanks