usually secret information used as input to various kinds of cryptographic algorithms, like encryption, signature, MAC, to select the concrete transformation done by the algorithm.

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Key material leak from initialized cipher?

Let's imagine that cipher (say AES256 in CBC mode) is initialized when application starts: ...
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2answers
178 views

Why do 1st and 3rd key have to be the same in 2 key 3DES?

From this answer: However, that wasn't the only situation they had in mind; they also considered the case where someone implemented 2 key 3DES in hardware (which the first and last subkeys ...
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1answer
136 views

Private and Public Keys

I have a very basic understanding of encryption and the encapsulation process, but for the life of me I can't grasp how public keys and private keys work, how they're made, and how they're exchanged. ...
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1answer
155 views

For a given PlainText-CipherText pair how many valid keys are there in AES?

For $PT\in \mathbb{M}$ and $CT\in \mathbb{C}$, let $\mathbb{F}=\{f|f:\mathbb{M}\rightarrow\mathbb{C}\}$ be the collection of all functions from $\mathbb{M}$ to $\mathbb{C}$. Then AES encryption under ...
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2answers
116 views

Is this a correct way of use symmetric encryption?

If I want to encrypt some block of text in AES, but at the time of decryption I don't have a way to check if the symmetric key is the correct one. So I: Generate a randomKey, and use that to encrypt ...
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3answers
59 views

Which method to generate one time password?

I'm looking for a concrete algorithm to generate one time passwords. The situation is as follows: Alice and Bob exchanged a passphrase over a secure channel in the beginning. They want to ...
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1answer
65 views

How to key an HMAC with keys from separate mutually untrusted parties?

The problem is as follows: There are two parties, both of whom would like to HMAC a message with a key. Although the keys are known to one another, both parties do not trust that the other one ...
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2answers
169 views

Parity of an encrypted key

Does encrypting a double-length 3DES application key (that has an odd parity) under a double-length 3DES zone master key (also with an odd parity) affect the parity of the application key?
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121 views

Algorithm to transform plaintext to a key of desired keysize, when using input plaintext as key for FPE?

Using a format preserving encryption scheme that uses AES internally as its block cipher, for a plaintext that I encrypt I want to use that input plaintext as the key. However using AES-128, my ...
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34 views

Hiding the identity of a party within the Kerberos authentication scheme

In the Kerberos authentication protocol, as described here: would it be safer to replace step (1) with: $$ A \rightarrow T : A, E_{K_A{_{T}}}(B, N_A) $$ so that a passive adversary does not know ...
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1answer
98 views

Can a billion elliptic curve keys be generated on a laptop in less than an hour?

I want my application to generate an EC key pair. The first four bytes of the sha256 hash of the public key should contain a known IP address. As hashes are one-way functions, I need to brute force ...
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2answers
167 views

HMAC key storage for a web app?

If one is going to use an HMAC, I.E: http://php.net/manual/en/function.hash-hmac.php, where exactly are they storing the key? Without some sort of secure storage (i.e not in a local file or code), I ...
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0answers
25 views

Raw /dev/random output for keymat [duplicate]

Noob question: It is my understanding that the raw output from non-blocking /dev/random (where the kernel's entropy_avail estimate is equal to or greater than the number of random bits required) ...
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3answers
309 views

How to protect key in software

I need to encrypt/decrypt data from my software by AES, the problem is how to make the AES key secure, there is no HSM, should I hard code the key in my code? It seems that a hacker can read the key ...
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1answer
55 views

For hardware encryptions, is it possible to know the key by analysing the hardware?

For example, Square reader uses hardware encryptions when swiping credit cards. Is it possible to know the key that is used by the hardware encryption cipher by analysing the hardware circuitries? ...
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1answer
54 views

Hash functions vs. keyed hash functions in the context of private key generation

I'm designing a key distribution mechanism and have thought of using a securely generated/acquired private key as a seed for a sequence of private keys to be distributed to a number of users using a ...
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2answers
110 views

Is it safe to initialize secret keys by just reading /dev/random on Linux?

For a software, I don't want the user to choose weak keys, so I plan to just read the needed number of bytes from /dev/random to create the needed secret keys. Is it safe to do so?
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0answers
21 views

Does the length of the keyword used for keytable for Playfair matter?

So for Playfair, we choose a keyword and put that in the keytable with no duplicates. Then, we fill the rest of the table with alphabets in order that are not in the keyword without 'J'. Does the ...
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2answers
68 views

Diffie-Hellman secret key choices

I'm trying to understand why the secret keys used by Alice and Bob in Diffie-Hellman are $a,b ∈ ℤ∗p$. Say $a$ is $p - 1$, wouldn't the transmitted $g^a$ be 1 mod $p$ by $FLT$? Now anytime a ...
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2answers
63 views

How to generate backup key for PBKD functions?

I would like to encrypt some files using AES, Ill derive key from password using some standard PBKD function and use that as AES encryption key. My question is, if user forgets the main password, ...
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2answers
115 views

Determine if a public key point y is negative or positive, odd or even?

Take an elliptic curve cryptography public key (x, y) and its additive inverse (x, -y). How do you identify which is the positive point and which is the negative point? Examples: Private key 1 -> ...
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2answers
75 views

Is there a standard format for compact 56-bit DES keys?

DES keys are traditionally stored as 8-byte blobs, with only the high 7 bits of each byte being meaningful to the algorithm; the low bit of each byte is set so that the population count of the byte is ...
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2answers
385 views

Secure method for encrypting 32 byte private keys

I am using 32 byte EC private keys on the client side of a web application. These keys should be securely stored on a server database. The keys should be encrypted (AES) before being sent to the ...
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1answer
104 views

Double Encryption Using same key

I am new to crypto and wondered what would happen when we encrypt twice using any algorithm and the same key. Consider two block ciphers A and B. We generate the ciphertext as c = A(B(m)) for any ...
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1answer
197 views

Determining if a ciphertext can be decrypted

I want to know what the state of the art in the following cryptographic problem is. Assume a public channel on which encrypted messages are exchanged, using symmetric key encryption. I hold a couple ...
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1answer
118 views

Two rounds of SHA-256 HMAC?

In a project we are working on, we have two applications within our datacenter that exchange messages. The messages are protected by an HMAC, and the secret key is stored on a SafeNet device. Update ...
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2answers
82 views

Possibility of the encrypted text being the same as the supplied plain text! [duplicate]

I was learning DES when it occurred to me that there could be a possible case where a (key, plainText) pair could result in an ...
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1answer
85 views

How can I handle the situation if key size is less than 64 bits in DES?

If the data is not a multiple of 64 bits, then I can use padding. I know that it is not secure. But if the key is less than or more than 64 bits, should I ask the user to enter the key again, or ...
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1answer
95 views

Is a 256 bit HMAC-SHA256 key compromised if the tail is used for identification?

Using a truncated hash of a key seems to be a safe way to identify the key (i.e. key fingerprint), but what about truncating a key itself in the case of HMAC-SHA256? Example: ...
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2answers
158 views

Is entropy being lost when the hash of a secret has a specific format?

Bitcoin's mini private key format works by brute forcing random data to produce a secret so that when appending ? and then hashing with sha256 it will produce a ...
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1answer
38 views

Is hashing data with dynamic keys still worth effort?

some years ago it took long time to "decrypt" hashes because they took slow cpu to brute force. Nowadays they use graphic cards for stuff like this and can do this most time in less than 20 Minutes ...
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2answers
270 views

Can a 1 byte difference in AES 128 bit keys make huge difference in output?

If we take some randomly generated key of AES-128 and we change any random 1 byte of that 16 byte key, will this make huge difference in the AES cipher text generated over same input string? Does ...
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0answers
31 views

Encrypt with K1, K2 and decrypt in opposite with K2, K1 [duplicate]

When using symmetric cipher, does the following statement holds: E(x, k) means encrypting x with key k in ECB mode ...
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1answer
471 views

Dan Boneh's Cryptography lecture - problem with 802.11b

I am going through Dan Boneh's Cyprography lectures on Coursera. In Lecture 6 https://class.coursera.org/crypto-010/lecture/6 At 7:30 minutes, he discusses the problems with 802.11b design. I ...
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3answers
593 views

Why does an algorithm need a keyspace?

Why does an algorithm need a keyspace? I thought the person encrypting would define his/her own key.
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1answer
284 views

Discrete Logarithm (512 bits numbers) - Find exponent parameter

I'm trying to resolve a discrete logarithm equation: $$y = g^x \bmod p$$ Every parameter is a 512-bit number. I know the values for $g$, $y$ and $p$ and I need to find the $x$ value. Finally, I know ...
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1answer
310 views

How are subkeys, in Feistel block ciphers, derived for each round?

I'm bit confused about the subkeys that are used in Feistel ciphers. I know that all the subkeys ki are derived from the main key K, but how? Say I have a simplified Feistel block cipher of i rounds, ...
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1answer
53 views

Cardinality of the key space $\{0,1\}^\ell$

Imagine we have a scheme whose key is chosen from the set $\{0,1\}^\ell$. My question is: What is the size of key space for this scheme?
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2answers
85 views

Brute Force on Key

If you are brute forcing a key and trying trillions of combos, how will you know when you accidentally hit the right answer? Clearly you can't look at each decoded answer to see which "looks right".
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1answer
106 views

Encryption through multiplication of encoded key [closed]

Yesterday I finished programming my own encryption program. It is using an input and a key. Here are all the steps it is going through. For an example, let say the ...
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4answers
670 views

Why don’t all AES encryption tools produce the same key from the same password?

Alice and Bob meet regularly. They have agreed face-to-face a 128 bit password which they want use to encrypt/decrypt emails written between them. They decide to use 256-bit AES. Alice wrote her ...
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1answer
216 views

How to calculate RSA CRT parameters from public key and private exponent

Given the public key (n, e) and private exponent (d), how to calculate CRT parameters (p, q, dP, dQ, and qInv) of this RSA key pair?
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1answer
73 views

Compacting a substitution cipher key

In a substitution cipher, I recieve 3 bits and than I return another 3 bits. The key of this cipher could be a matrix represented as: ...
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1answer
120 views

XOR = Best encryption? [duplicate]

If you have a TRULY random key (in binary) and you have a text (in binary) that you want to encrypt. Can you simple XOR the key and the text? Is that secure? How secure?
2
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1answer
150 views

Key Check Value standard pratice for asymetric cryptography?

I'm looking for a standard, or sound industry practice, for the equivalent of a Key Check Value, applied to the private key of a public key algorithm, like ECDSA. For DES or 3DES keys, practice (as ...
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0answers
321 views

Proper way to generate symmetric keys [duplicate]

I'm trying to educate my self in key management, how to store them, how to generate them, how to use them properly. I've been trying to find how you would generate a key for symmetric encryption (say ...
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4answers
90 views

Definition of the term “key”

I've looked in many places (NIST, text books, online resources) and I cannot find an answer to the definition of the term "key" from a semantic point of view. Is it the "key" to cipher-texts (i.e. ...
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47 views

Generating interactive, secure multiple ECC key pairs deterministically

In Elliptic Curve Cryptography (ECC) assuming user A has a private public key pair of $S$, $P$ accordingly with generator point $G$ which as we know is: $$P=S*G$$ Assuming that user A wants to ...
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229 views

correct usage of keys and nonce

I've being studying up on AES, GCM, CBC, HMAC and a lot of other primitives and am somewhat ( a little bit, perhaps) familiar with them however I am still a bit weary on the use of the keys and nonce. ...
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2answers
359 views

Key space vs Cardinality of 1024-bit RSA

I have been trying to figure out the encryption key space, and cardinality of 1024-bit RSA. From my understanding, the key generated from 1024-bit will be primes greater than $2^{1023}$ but less than ...