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    Cryptography German Enigma from WW2. I never thought I’d see one in person.

    April 08, 2019

    Cryptography German Enigma from WW2. I never thought I’d see one in person.

    German Enigma from WW2. I never thought I’d see one in person.

    Posted: 07 Apr 2019 10:10 AM PDT

    I'm in a course titled encryption and feel like I have barely learned anything.

    Posted: 08 Apr 2019 12:32 AM PDT

    I need to go over some stuff over the summer. I want to dedicate atleast 10-20 hours to actually studying what I could of learned this semester.

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    I just write off the notes. I forgot what a block cipher was, all i know is that it is a determinstic function that encrypts something. That's the only way I can freaking describe it.

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    Is there a way I can learn over the summer? Can a book be enough to help me actually learn something? I can't find an online course on udemy.

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    I did learn some stuff but not alot.

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    Can someone answer this question for me though if you can, when your teacher lectures say a few weeks ago used to explain something. Could you even remember what it was? Like I always forget.

    submitted by /u/velociraptor90
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    Feistel Cipher Proof

    Posted: 07 Apr 2019 06:32 PM PDT

    How can I prove that a two-round Feistel cipher using the functions f, g in that order results in a different permutation of the set of possible inputs (x, y)?

    submitted by /u/willjmill3
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    Block Cipher Modes of Operations

    Posted: 07 Apr 2019 04:17 PM PDT

    I am new to this subject and could use help understanding the encryption process using modes of operations. For example, I have a Feistel cipher with block length 2, and a key that is a pair of mappings σ, τ on the set of symbols. To encrypt (x, y) we use:

    • x ′ = y, y′ = x + σ(y),

    and then,

    • x ′′ = y ′ , y′′ = x ′ + τ (y ′ ).

    if σ(x) = x2 , τ (x) = x3 , how do I encrypt a the string 777777 using Electronic CodeBook mode?

    submitted by /u/willjmill3
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    ED25519 question

    Posted: 07 Apr 2019 05:59 AM PDT

    ED25519 key generation is done by generating random 32 seed, then hashing seed with sha2-512 where

    first 32 bytes are used as private key and derived public key from it, other half of hash is used as initial fixed nonce used in signing process.

    Replacing the nonce with random one for each signing will not break verification of signing process.

    What are pros end cons if nonce is replaced with random nonce for each signing ?

    Edit:

    Key generation

    seed = random 32-byte string (a,z) = sha2-512(seed) A = a*B

    Signing process

    ​

    r = sha2-512(z,M) R = r*B h = sha2-512(R,A,M) S = r+h*a signature = (R,S)

    I would like to implement into signing process next changes that would not affect verifying process.

    nrn = new random nonce c = sha256(z|nrn); r = sha2-512(c,M) R = r*B h = sha2-512(R,A,M) S = r+h*a signature = (R,S)

    ​

    so for each signed messages z is replaced with different value.

    I trying to come into conclusion how much is this necessary, does it improve security and how safe is.Since I am an beginner in cryptography, I would like to see opinions of more experienced minds first.

    ​

    submitted by /u/zninja-bg
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    [Python 3] [PyNaCl] - Implementing Diffie-Hellman Key Exchange, Perfect Forward Secrecy, and Identity Verification. Is it possible?

    Posted: 07 Apr 2019 08:16 AM PDT

    Currently, I am working on a project in Python which is dependent on secure communication. To accomplish this, I am currently making use of the PyNaCl library built off of (big surprise) NaCl. I'd like to make this communication between parties as private and secure as possible. The way I've somewhat resolved how to do this after a bit of research is by having:

    • Both parties locally generate an asymmetric public/private keypair.
    • Use these keys to authenticate each other's identities before anything else occurs (This is currently done, probably insecurely, by exchanging each other's public keys in plaintext. Help GREATLY appreciated).
    • Following authentication, use Diffie-Hellman Key Exchange to securely generate and agree on a shared symmetric key. (I have no idea how to implement this in PyNaCl, or how to then take this key and plug it in to PyNaCl's symmetric key communication. Help once again GREATLY appreciated).
    • Messages are sent using the standard built-in PyNaCl symmetric key communication methods, but specifically using the key agreed on during the Diffie-Hellman exchange. (See above parenthesis).
    • After receiving a message, the key is scrubbed and we start all over again from Step 2.

    Any assistance that you all can provide in either correcting my procedure and/or explaining how I can accomplish this in PyNaCl would be extremely appreciated. My only other question would be that since we are trying to use this potentially in a mobile device environment, would this absolutely swallow data? Thank you for any help you can provide in advance, and please bear with me if I ask stupid questions. I'm not brand new at this, but I'm far from an expert.

    submitted by /u/GettingKittyWithIt
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    Why are there two RSAs for Kleopatra PGP and what is the "Valid Until" thing about?

    Posted: 07 Apr 2019 08:04 AM PDT

    Basically title says it.

    There are two RSA check boxes to check.

    Also what is the valid until thing about? Like literally how does it work? Since when do signature algorithms automatically expire after a date?

    Also literally what is Authentication checkbox in there for?

    Edit: Here's screenshot: https://imgur.com/MkQ0Y2g

    submitted by /u/_Hormoz_
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    EasyPGP — library for mobile devices

    Posted: 06 Apr 2019 10:54 PM PDT

    Hi all,

    Just wanted to share a small library I've made — EasyPGP

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    Its goal is to provide simple cryptography primitives usable across iOS/Android apps and their backend servers.

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    EasyPGP is a tiny wrapper around Go's OpenPGP which is usable on mobile platforms via gomobile. It also has protobuf description for messages, so it can be easily integrated into gRPC.

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    I'm also wondering whether this is sane approach, as there is NaCl/libsodium, but those seemed somewhat more hard to use and there was not consistent encoding format(there is armoring in PGP).

    submitted by /u/otsutstvuet
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    Name of process where you exchange information secretly over a public channel by using keys

    Posted: 06 Apr 2019 10:17 PM PDT

    Figured this subreddit would have the best chance at knowing what I'm talking about:

    I witnessed this being done on Yik Yak when it was a thing and can't remember what it was called. One user posted a key, some number, and another user does something with that key and returns with another number. The original user does something with that new number, and the end result is they both have a new key that each other are aware of but nobody who was observing them would know.

    Anyone know the name of this process?

    submitted by /u/Shuai_Nerd
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