# Tag Info

5

The standard way to do this is with a hash list. That is, you would hash each of the messages $m_i$ to produce a hash $h_i = H(m_i)$, and then combine all the hashes and hash them to obtain a master hash $h = H(h_0 \| h_1 \| h_2 \| \dots \| h_n)$. Finally, you can e.g. digitally sign the master hash to prove that the hash, and by extension all the ...

3

I'm trying to get my head around how the crypto solves this problem. It doesn't. You need to trust the platform you use to do the signing. For instance, my bank has replaced the "signature" generation device that I previously used with one that displays the actual transaction, so I don't have to trust the information on the computer screen that much.

2

ECKEY object may contain: Group Private key Public key Both Group and Private key are needed to be able to calculate signature. It is most convenient to use generic ECKEY object (from API perspective), as it easy to e.g. convert between commonly used PKCS#8 PEM encoded EC private keys and ECKEY objects, and because just a BIGNUM would not be sufficient. ...

2

The short answer is that there's no link between your physical signature and any cryptographic signature. Indeed, from the high-level description of how DocuSign works and their security manifesto there's no reason to believe that any cryptography goes into the signature process itself. Note that “signature” is an overloaded word. In this post, I will refer ...

2

You have to show that you can use the account. You cannot prove it offline, without accessing the account (or storing public information there) or else anyone else could produce the same "proof". Normally proof of ownership of a web page is done by the other party producing some random value and you publishing that value on the page. That would work here ...

1

Suppose you have an asymmetric algorithm that creates a 48-bit signature. Then an attacker can simply test possible 48-bit signatures and find one that verifies in $2^{47}$ tries on average. Even with a relatively slow asymmetric algorithm that would be feasible, especially if the attacker can test the same signature for multiple tokens. And that is only a ...

1

Here is an explanation of step 4. Look at Figure 2 of the paper. Lets say $y_s$ is $y_3$ at 6 o'clock. Start at 12 o'clock and calculate going clockwise until you arrive at 6 o'clock. Denote the result by $r$. Start again at 12 o'clock and calculate going counter-clockwise until you arrive at 6 o'clock. Denote the result by $l$. Now $l =r \oplus y_s$, which ...

1

We assume an RSA signature scheme with appendix where the signature of message $M$ is $S=\left(\operatorname{MD5}(M)\right)^d\bmod N$, and the verification procedure checks that $0\le S<N$ and $\left(S^e\bmod N\right)=\operatorname{MD5}(M)$, with $e=3$ (or other relatively small odd $e\ge3$). Eve somewhat got $k$ rightful signatures $S_i$ and perhaps the ...

1

The premise that you don't need to split the messages before encryption is incorrect. Given that there are schemes giving (partial) message recovery for signing also means that that premise is incorrect as well. The message doesn't need to be split up before signing (which includes hashing), so that premise, finally, is also incorrect. Encryption operation, ...

1

The web site of https://ellipter.com says, they are using encryption.

1

A few things. First of all, MD5 is broken, and no longer suitable for cryptographic purposes. Instead, prefer newer algorithms, like those from the SHA-2 family (SHA-256, SHA-512, etc). Second, the term "signature" in cryptography is defined more narrowly than you would expect. It specifically refers to situations where there is a public key (the ...

1

First, there is no way that crypto can keep an attacker from manipulating the data that is shown to the user. to prevent this, you have to trust some part of your hardware, at least the screen that views the data and some chip inside that can do some crypto. Moreover, digital signatures alone will not solve this problem as the merely capture signing a ...

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