# Questions tagged [message-recovery]

Message recovery is a feature of some digital signature schemes, whereas some or all of the message signed is embedded in the signature, recovered as part of signature verification, and thus needs not be transmitted.

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### How to encrypt using private key for ECC

As we know, ECC using $C_2 = r \cdot G, C_1 = M + r \cdot G$; and decrypt with $M=C_1 - K \cdot C_2$. And sign using point $X$: $X = k \cdot G(x_0,y_0)$. \$r = x_0 \cdot K; s = 1 / k \cdot (M + r \cdot ...
99 views

### message in mars lander parachute [closed]

I think there's a msg in the parachute of the mars lander , the guy in the vid seems to hint at it I converted this to binary with red=1 and white=0 starting from the three all-red sectors in the top ...
182 views

### How can RSA be used to compactly sign and encrypt?

How can RSA be used for digital signature with message recovery and encryption, providing transmission of a small message with confidentiality and authentication simultaneously, small cryptogram size, ...
100 views

### Understanding why Semantic Security implies Message Recovery Security

I am stuck in the proof where it says $$p_0=1/|M|$$ , I just do not understand how we can infer this equality. Also, am I right in understanding that B is defined as choosing his two messages at ...
61 views

### An insecure signature with message recovery, Dan Boneh

Someone can help me to resolve this questions from the book of Dan Boneh (University of Standford)
85 views

### Elgamal security if same key used twice

Assume that user A sends to user B a message, unencrypted, and signs it with an Elgamal signature. Can some adversary, call it C, who eavesdrops, learn the private key if user A signed both messages ...
743 views

### 521-bit ECC keys are the same strength as RSA 15,360-bit keys

521 bit ECC uses key sizes 7.5 times smaller than the RSA standard while offering encryption that is magnitudes more secure. An RSA 2048-bit key's secure enough for banking, but a 521-bit ECC key is ...
52 views

### Dining-Cryptographer Net (DC-Net) Scheme that Handles Collisions?

[Question edited at the request of Mods] I recently became fascinated with the elegant and simple solution that Chaum proposed for the Dining Cryptographers problem. If you are unfamiliar, please ...
221 views

### In ISO/IEC 9796-2 (signature with message recovery), why are some message representatives bigger than the modulus?

I have implemented signature scheme 2 from ISO/IEC 9796-2 in C using OpenSSL for the underlying crypto operations. To generate the message representative (F in the ...
436 views

### Why ISO/IEC 9796 (signature with message recovery) instead of just encrypt the short message with private key?

I've had a look at “Practical Cryptanalysis of ISO/IEC 9796-2 and EMV Signatures” and read the very good answer https://crypto.stackexchange.com/a/17846/59673 and I understand that signature and ...
258 views

### Build a cipher that is secure against message recovery attack but not semantically secure

I know the definitions of both of the securities (against message recovery and semantic), but I don't know how to actually build a cipher that meets these conditions, I mean, I don't know how to ...
1k views

### RC4: Find the complete plain text of a ciphertext when we know part of the plaintext

I need to decrypt an encrypted file with RC4 to answer to a Internet challenge. The file in question is a dump of a Teensy ROM and it is completely encrypted. Luckily, it looks like it's a standard ...
367 views

### Cryptanalys of “bad” RC4 implementation

I need help of cryptanalyzing a "bad" RC4 implementation to recover an encrypted text of 13742 bytes. I don't know the key and this implementation does not utilize the drop-n routine. But, I know ...
141 views

### Minimizing size of signed message with discrete-log scheme

How can we sign a small message with a discrete-log scheme so as to minimize the size of the whole signed message? Detailed objectives, notation: It is of paramount importance to minimize the total ...
806 views

### Message-Recovery variant of Ed25519 signature?

What would be a Message-Recovery variant of the Ed25519 signature scheme? Ed25519-MR should be simple to use, fast, with a strong security argument, and striving to stay out of the patent minefield, ...
2k views

### Forgery attack against Textbook RSA with simple redundancy

I know how to forge vanilla Textbook RSA message signatures (easy). I've learnt that by adding a good redundancy to the message, it cannot be forged anymore. How can one add redundancy so that the ...