Linked Questions

3
votes
2answers
1k views

HMAC does it matter if I chose the cipher text or the plain text as the message? [duplicate]

I am using HMAC to create a message authentication code. My question is, does it matter if I use cipher text + encryption key or ...
0
votes
1answer
583 views

What is the advantage of Encrypt-then-MAC over Encrypt & MAC separately the plaintext [duplicate]

For secrecy, authentication & integrity, you can either use CipherText = Encrypt(PlainText) Signature = Hash(PlainText) CipherText = Encrypt(PlainText) Signature = Hash(CipherText) Either ...
0
votes
0answers
75 views

Encrypted vs unencrypted digital signatures [duplicate]

Is there a difference in terms of security between An encrypted stream of bits obtained by encrypting a plaintext concatenated with it's signature $ C = E_k(plaintext||\sigma)$ where $E$ is a ...
125
votes
6answers
88k views

Should we sign-then-encrypt, or encrypt-then-sign?

Frequently, we want to send messages that are (a) encrypted, so passive attackers can't discover the plaintext of the message, and (b) signed with a private-key digital signature, so active attackers ...
61
votes
3answers
92k views

Why shouldn't I use ECB encryption?

I'm using Java to generate encrypted strings, and I get this warning at build time: ECB encryption mode should not be used So I'm wondering why I shouldn't use ECB and what I can use instead?
67
votes
3answers
21k views

Signal vs Telegram in terms of protocols?

Some time ago, the question was asked in chat, why MTProto (Telegram's protocol) is supposedly worse than Axolotl (Signal's protocol) as both protocols have been the inventions of their respective ...
19
votes
4answers
8k views

Why is OCB-AES mode not becoming a standard for authenticated encryption?

The OCB mode of authenticated encryption (used for example with AES) is the fastest way to provide authenticity and confidentiality without having to strive into questions like: Encrypt then MAC, MAC ...
11
votes
9answers
684 views

Physical analogue for MACs

What would be a good analogue with which to describe Message Authentication Codes to a person who has little to no understanding of cryptography? For instance, a vault is a reasonable analogue for ...
10
votes
5answers
6k views

Tamper-proofing log files

Problem Overview I want to securely store log files so the contents are secret, and they can't be modified without detection. The files will be encrypted using authenticated encryption (AES in GCM ...
6
votes
1answer
34k views

Why is padding used in CBC mode?

I am newbie to CBC crypto: When I try decrypt the cipher text to recover the plain text, things are not going smoothly as I face some issues in the decryption process with padding and not obtaining ...
3
votes
3answers
9k views

How to use HMAC-SHA1, HMAC-SHA2 in conjunction with AES

I understand how to compute HMAC-SHA1, HMAC-SHA2 etcetera. Please explain why/how is the resulting HMAC value is used in conjunction with AES for encryption/decryption and signing/verifying. In ...
20
votes
1answer
2k views

Why choose an authenticated encryption mode instead of a separate MAC?

What are cryptographic reasons to choose an authenticated-encryption mode of operation (such as GCM) over a traditional encryption mode plus an independent MAC, or vice versa? Assume there is no ...
9
votes
2answers
2k views

Does secure hashing imply secure symmetric encryption?

I was wondering if the mere existence of a (by some definition) secure cryptographic hash function immediately implies an equally secure symmetric encryption scheme. By my understanding, one could to ...
6
votes
6answers
2k views

Is there an authenticated encryption scheme where the recipient can attribute the message to a single sender?

With a standard authenticated encryption scheme (or MAC), Alice and Bob share a symmetric key. When Alice sends something to Bob, Bob can check that it is authentic. At that point, Bob can deduce ...
11
votes
2answers
2k views

Random data CBC padding scheme?

When using AES in CBC mode, padding is required when the last plaintext block has not the length required by the cipher. Let's say $k$ mode bytes would be required to fill the block. My idea was to ...
7
votes
3answers
2k views

Encryption-then-encode or encode-then-encryption?

I have this question in which I m struggling. I have read in many sites about encrypt-then-mac etc. If the confidentiality for transmission is needed, discuss the feature for the order of encryption ...
13
votes
1answer
4k views

Why do we encrypt-then mac but sign-then-encrypt?

This question was asked in comments on my answer to should we sign then encrypt or encrypt then sign. I think posing the question as a separate entity is best, so: The general advice for applying ...
7
votes
1answer
1k views

Is Encrypt(m||k2, k1) secure authenticated encryption?

I don't fully understand the need for MAC algorithms to authenticate encrypted messages. As I understand, the standard is to send something like $\mathrm{E}(m,k) \| \mathrm{MAC}(m,k)$ where $E$ is an ...
3
votes
2answers
5k views

AES + CBC encryption for a stream of UDP packets

I am developing an application that is based on UDP, and I need to send a stream of packets. As you can imagine, packets can get lost or corrupted. I need to make sure that the content of those ...
10
votes
1answer
3k views

The difference between MAC algorithms and what to use

I've been looking into message authentication codes and found several ways to create integrity for a message. I know of the following algorithms: HMAC, this can use any cryptograhpic hash function ...
5
votes
2answers
2k views

Why does TLS do Authenticate-then-Encrypt instead of Encrypt-then-Authenticate?

Encrypt-then-Authenticate (EtA) seems to generally be considered the better option, compared to Authenticate-then-Encrypt (AtE) (see this Crypto.SE question, for example). The people writing the RFC ...
5
votes
2answers
2k views

During padding oracle attack (CBC), how is first byte of plaintext block is obtained?

Imagine conducting a padding oracle attack against CBC mode with 16-byte length blocks, and PKCS#5 used for padding. You start, as always, revealing the last byte of plaintext. Then you iteratively ...
9
votes
1answer
5k views

Does adding a salt to the message before HMAC processing add any security?

An HMAC function is designed to verify message integrity, i.e., that the message has not been tampered with. It is generally (always?) implemented by using a hashing function ...
2
votes
3answers
2k views

How does one provide a secure and authentic communication channel?

Let assume two participants Alice and Bob who perform a given protocol which is a sequence of messages exchange between them. My question is: How can I provide a secure and authentic communication ...
2
votes
1answer
7k views

Why should a signature use PSS padding in RSA?

Suppose I send a message using AES (private keys already negotiated securely) and I send a hash of this message using RSA (encrypted with private key) with OAEP to verify the authenticity and ...
10
votes
1answer
2k views

For a one-time pad, which MAC method is information-theoretically secure?

In the the main post about MAC methods it mentions a few methods: Authenticate And Encrypt: The sender computes a MAC of the plaintext, encrypts the plaintext, and then appends the MAC to the ...
4
votes
2answers
1k views

Security issues of a MAC-then-Encrypt-then-MAC approach?

Encrypt-then-MAC does provide ciphertext integrity, but no plaintext integrity. With MAC-then-Encrypt it’s the other way around: Plaintext integrity but no ciphertext integrity. What comes to mind is ...
5
votes
2answers
1k views

Why is MAC using nonce+message+hash(nonce+message+identifier) not the standard?

Given that we know that nonce + message + hash(nonce + message + mac-key) all inside the encryption makes it possible to detect if any bits of the message have been ...
-2
votes
1answer
3k views

Hash-Then-Encrypt or Encrypt-the-Hash?

My question is would it make any difference if I hash a block of data and then encrypt it using RSA is most secure to do the reverse? The question is about Site-To-Site transmission where the ...
7
votes
2answers
757 views

Is there a companion algorithm for OTP to ensure integrity and/or authentication?

One-Time Padding is (theoretically) perfect encryption algorithm. Let's assume that these problems are solved: Fast generation of independent and identically distributed random variables Perfect key ...
1
vote
2answers
4k views

HMAC vs Encrypted Hash

What is best to use (for message integrity) between… AES(Data) + HMAC(Data) AES(Data + HMAC(Data)) AES(Data + Hash(Data)) …and why?
-4
votes
2answers
446 views

AES_256_ENCRYPT_CTR(key, sha-1(plainText)+plainText) VS AES-GCM, which is more secure? [duplicate]

What if we encrypt sha-1 hash of the plain text, along with the plain text using AES-256 in CTR mode? How much future proof the above method would be in comparison to AES-GCM or any other method ...
5
votes
1answer
1k views

CBC-MAC just to verify integrity

I have a message and I want to verify its integrity and authenticity. I have a shared secret (key) that is not used for other encryption. Is it safe to send a plaintext message containing all the ...
0
votes
1answer
5k views

AES standard C library implementation

I'm working to implement AES (128/256 - either) on one of the RISCV ISA processors & later improve performance by introducing a custom instruction in RISCV ISA. I'm a crypto newbie and plan to ...
6
votes
2answers
2k views

Encrypt-then-MAC Confidentiality, Integrity and Authenticity

Does Encrypt-then-MAC provide equal confidentiality, integrity and authenticity as other constructs such as EAX? If yes, how do I go about using it? My current understanding is: E = encrypt(...
2
votes
2answers
2k views

Encrypt-then-MAC paradigm

I read that the Encrypt-then-MAC paradigm is provably secure. From what I understand, when using for example AES for encryption and HMAC_SHA256 for MAC generation (and the keys $K_1 \neq K_2$), this ...
3
votes
1answer
2k views

How is padding oracle attack mitigated by encrypt-then-MAC?

Let us suppose Alice sends a message to Bob. As far as I know, the most popular scheme of MAC-then-encrypt is as follows: Alice computes the HMAC of the plaintext using her private key, and then ...
1
vote
1answer
2k views

Establish a secure connection between a Bluetooth Low Energy device and an Android App using ECDH

Im very new to security and trying to learn how to establish a secure connection between a android application and a Bluetooth Low Energy device with limited hardware performance. The procedure: App:...
3
votes
1answer
4k views

AES-CBC then SHA vs AES-GCM for encrypting and authenticating a web token

I am trying to have something like JWT but kinda ad hoc and encrypted. The token itself is simply a stringified JSON that contains the user ID and Unix timestamp. Now, I tried to use AES-128-GCM, ...
3
votes
1answer
1k views

Using checksum instead of hash for authenticating ciphers

Lets assume for a specific situation we cannot use authenticated encryption like GCM ... If we were to use CTR, what would you think of using a checksum on the plaintext then encrypt the whole. The ...
1
vote
3answers
2k views

Counter based cipher using HMAC-SHA-256

After trying to invent my own AES mode, I decided to just implement something that's known to work, namely CTR mode with HMAC-SHA-256. From what I understand, I can use the IV as a counter, and the ...
3
votes
2answers
2k views

Private RSA key for HMAC key

I am creating software tokens for future request authentication, and I want to use an HMAC for the token to make them tamper-resistant. To ensure I can check the HMAC later I need a secret, persistent ...
-4
votes
1answer
2k views

bruteforce on aes 256 cbc mode [closed]

i have a series of encrypted text , they encrypted by aes 256 bit cbc mode for every encrypted text there is an iv that i have them also and i know its algorithm is aes 256 bit cbc mode i can ...
2
votes
2answers
1k views

Avalanche noise RNG for one-time pad use

I came across this little HRNG widget and was really intrigued as I have been looking for a decent but afordable source for truly random bits to use in a one-time pad. The question is, would a HRNG ...
5
votes
2answers
1k views

Random session key + predictable IV

I'm using Blowfish in a toy Diffie-Hellman communications scheme. Random session keys are generated for each connection. In this case I can simply feed a null array to the IV right? The same ...
0
votes
2answers
170 views

Is CTR more secure than CBC?

In cryptography, a block cipher mode of operation is an algorithm that uses a block cipher to provide information security such as confidentiality or authenticity. A block cipher by itself is only ...
7
votes
1answer
947 views

Security of a simple AEAD construction

Introduction I want securely communicate with a small 8-bit device which has a very limited program program memory (Arduino Uno - 32K). My goal is to minimize code size and RAM usage. There are ...
2
votes
2answers
2k views

Is HMAC necessary if the AES ciphertext of a message includes the CRC of the message?

I've seen that encrypting an image with AES-CBC then calculating the HMAC-MD5 value for authentication is a somewhat common and sound way to secure data. Alternatively, can I just calculate the CRC of ...
2
votes
2answers
2k views

Some questions about encrypting (AES) a file with password

I'm relatively new to encrypting, and I have some questions. I intend to write a standalone C# program that will write and read an encrypted file with sensitive data using a password entered by the ...
2
votes
2answers
296 views

Is E_k(M)||H(m) form of MAC secure?

Would this encryption and signing scenario be considered tamper-proof? ...

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