Combination of encryption and authentication in a way that ensures confidentiality and integrity.

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Does length prepending fix the key reuse problems with CBC and CBC-MAC?

As I hope everybody is well-aware, re-using the key for CBC-MAC and CBC is a really bad idea. Now, there's also the paradigm to prepend the message length to the CBC-MAC (as "associated data") to ...
3
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1answer
42 views

The solution of insert MAC in a ciphertext without Authenticated Encryption supported

From Should we MAC-then-encrypt or encrypt-then-MAC?, I understand I should do Encrypt-than-MAC, which the MAC included all the information such as IV and cipher text. After reading Why choose an ...
3
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1answer
92 views

Authenticated encryption with Signatures

I've given a CPA secure private key encryption scheme (wich gets to a CCA secure scheme or better to an authenticated encryption scheme, when i combine it with a given MAC) and a unforgeable public ...
3
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0answers
30 views

Authenticate encrypted seed for KEM + AEAD hybrid cryptosystem

Say I want to encrypt something using RSA / KEM and an authenticated cipher. I encrypt using the following scheme: generate random seed z using ...
3
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0answers
103 views

Can convergent encryption be turned into deterministic authenticated encryption with HMAC?

If you take a convergent encryption algorithm and replace the hash $H$ used to derive the key with HMAC-H, keyed with a secret key $k'$, does the resulting algorithm provide you with deterministic ...
2
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3answers
471 views

Can ECB mode really leak some characters?

In an Ars Technica article about Adobe's use of 3DES in ECB mode, there's a paragraph The passwords, according to password expert Steve "Sc00bz" Thomas, are encrypted in a mode known as ECB. That ...
2
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2answers
373 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
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2answers
323 views

secure embedded/microcontroller crypto using AES-ctr with hmac-sha2

The embedded device is a low-power 8-bit microcontroller (memory usage is constrained to about 10kb code, 1kb ram). As the device is battery-powered and manual service should be minimal, more powerful ...
2
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3answers
269 views

Encrypt-then-MAC: full random keys or keys derived from master key?

I have this scenario where I use Encrypt-then-MAC (AES256-CBC and HMAC-SHA256) with keys generated by a CSPRNG (specifically, SecureRandom in Java). I'd like to know which is better: Use the CSPRNG ...
2
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1answer
357 views

Does SpongeWrap (from the Keccak team) absorb ciphertext or plaintext?

I have been reading the Cryptographic sponge functions paper, but I'm still confused. Does Keccak in authenticated encryption mode absorb ciphertext or plaintext? Edit: Are there any test vectors to ...
2
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1answer
48 views

security of a block cipher mode of operation

Consider the following block cipher mode of operation: \begin{align} tag_0 &= mac\:key\\ plaintext_0' &= plaintext_0 \oplus iv\\ E(tag_0 | plaintext_0') = C_0 &= tag_1 | ciphertext_0\\ E(...
2
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1answer
636 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 ...
2
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2answers
258 views

Is there a point using GCM block chiper with Authenticated DH?

I'm delivering shared secret with DH exchange, using a static key for signing and an ephemeral for session, so is there a point using GCM for encrypting the data, or is a simple CBC/CTR block cipher ...
2
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1answer
531 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 ...
2
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1answer
178 views

ID-Secret Scheme

I have an ID-Secret scheme and I'd like to hear if there are any vulnerabilities present. Party 1 and Party 2 hold some credentials, an ID and a Secret. Party 1 Creates this message: ...
2
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1answer
84 views

Advantages of HS1-SIV over ChaCha20-Poly1305-SIV?

What advantages does HS1-SIV have over ChaCha20-Poly1305-SIV? I know that both use the ChaCha stream cipher, but I am trying to understand why HS1-Hash is a better MAC. Edit: To hide the Poly1305 ...
2
votes
1answer
137 views

Format preserving encryption FFX

In FFX mode the format of the ciphertext is same as plaintext. How does it ensure data integrity and authentication? Is there any bit flip attack in FFX mode? Is it malleable?
2
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1answer
274 views

Flaw in the security definition of *Stateful* Authenticated Encryption?

I'm in search of the correct definition of a stateful authenticated encryption scheme (sAE), and its related security notion. This has been treated several times in the academic literature, however, ...
2
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1answer
277 views

The security of an encrypt-and-MAC

I would like to know what is the security of an encrypt-and-MAC with different keys for each transaction For example: the one-time-pad with $k_1$ and the HMAC with $k_2$ $$C = M \oplus k_1\\ MAC = ...
2
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2answers
93 views

Is the security of an HMAC equally important as the security of the cipher itself?

I'm a little unclear on how hash based MAC works... So I would like to know, is the security of your hash function as important as the security of the overall cipher? Basically, if you can crack the ...
2
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2answers
127 views

3DES over Galois Counter Mode (GCM) for authenticated encryption

Is it possible to use DES or 3DES over Galois Counter Mode (GCM) to provide authenticated encryption? I haven't seen any implementation yet.
2
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1answer
167 views

Security of basic SHA256 MAC in an authenticate-then-encrypt scheme

I know the following construct is insecure if the MAC as defined below is appended to the encrypted message in an Encrypt then Authenticate (EtA) scheme. $k_1$: encryption key $k_2$: authentication ...
2
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1answer
172 views

Is AES-GCM length extension attack possible using authenticated decryption?

I am looking to encrypt a piece of data using AES-GCM with a full 16-byte GCM Tag and send it over the network using UDP. Is it safe to assume using the AEAD nature of AES-GCM that performing ...
2
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1answer
492 views

Encryption and HMAC key derivation

I'm deriving keys from a user-supplied passphrase for symmetric encryption using AES-256 in CBC mode with a HMAC for authenticity/integrity. My key derivation function currently looks like this: ...
2
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1answer
363 views

Authenticated Encryption of UDP packets

I am working on a UDP based file transfer protocol. Congestion Control, Resending of packages and other UDP challenges are dealt with - speedtests shows that the protocol is up to 10 times faster than ...
2
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1answer
78 views

Can we use the authentication tag as Nonce / IV for the next message?

Let's assume we're in some scenario requiring transfer of large amounts of data. This means we can only use AES-GCM chunk-for-chunk as its maximal size is restricted to a few GiBs. This means we have ...
2
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1answer
318 views

is this authenticated key exchange protocol sound? too complicated? obviously flawed?

(significantly reworded this question to fit better into crypto.se). I have static RSA keypairs for both sides and an encrypted transport that needs symmetric keys, and need to exchange session keys. ...
2
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0answers
62 views

StoredKey in Salted Challenge Response Mechanism (SCRAM)

In SCRAM (RFC5802, page 8) the client generates ClientKey to server, which is a derivation of the original password. This is communicated to the server in a secure ...
2
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0answers
211 views

What are the constraints on using GCM with a tag size of 96 and 128 bits

Say we want to use AES (or any other secure 128 bit block cipher) with GCM and a tag size of 96 or 128 bits. I'm assuming an AES key size of 128 bits and an IV size of 96 bits (the default). NIST ...
2
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0answers
49 views

How can I read the AE figures?

This question is rather simple. I've recently read the paper "Automated Analysis and Synthesis of Authenticated Encryption Schemes". On page 17 of this paper the authors provide three figures of ...
2
votes
2answers
273 views

Post-quantum authenticated encryption

It is well-known that the Grover's algorithm reduces cryptographic strength of symmetric ciphers to a square-root - e.g. AES-256 becomes only 2128 strong. However, these statements are always made ...
2
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0answers
168 views

Design requirements for a keyed hash function?

I am actually preparing for a cryptography exam, and I found a question asked by the professor in the class, below are the lines that I copied from the slide : Example: Let $Ek$ be the encryption ...
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2answers
228 views

How resilient to attackers with extreme resources available is this encryption method?

How could the following scheme be made more resilient to attacks capable of utilizing massive amounts of resources? Assume all random values are cryptographically secure. Key derivation: scrypt ...
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1answer
2k views

AES GCM symmetric encryption of data at rest in c#, ciphertext much longer than plaintext

I've written encryption/decryption routines using AES GCM. Code can be found here. I recently realized that the cipher text is longer than I believe it should be. It should add the tag and IV onto ...
1
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1answer
36 views

Would A5/1 with a much larger state be a good choice of stream cipher for hardware?

Would A5/1 with a much larger state be a good choice of stream cipher for hardware? Assume that a reasonable choice of MAC is made such as GMAC, with the first 128 bits of the stream cipher output ...
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2answers
133 views

Why can't NORX produce intermediate auth tags like Keyak can?

Why can't NORX produce intermediate auth tags like Keyak can? Keyak appears quite attractive because of this, but seems to be slow in the absence of hardware acceleration.
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1answer
210 views

Simplified Example of ECC to use in the classroom

I have come up with the following rudimentary example of how ECC relates to asymmetric keys. Is this a valid explanation of ECC and its relationship to asymmetry? To only be deciphered by the person ...
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1answer
456 views

Does RSA-OEAP have integrity and authenticity properties?

RSA-OAEP is IND-CCA2 secure (indistinguishable under an adaptive chosen ciphertext attack). Does it also have the INT-CTXT (integrity of ciphertext) and INT-PTXT (integrity of plaintext) properties? ...
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1answer
83 views

What should I think about these unique certificate serial numbers [closed]

I was looking at the serial numbers of the certificates for www.google.com and wordpress.com. Wordpress was listed by openssl as: 04:0B:D4:F8:25:88:C5 This serial is listed as the serial for both ...
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1answer
195 views

Is MAC-then-encrypt with stream ciphers secure?

While thinking about this recent question about a hash-then encrypt design, I reread the MAC-encrypt vs. encrypt-MAC question and noticed this answer quoting a paper showing that MAC-then-encrypt is ...
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2answers
75 views

Single-algorithm authenticated encryption

Are there any authenticated encryption methods that combine encryption and authentication, rather than useing a separate cipher and MAC?
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1answer
84 views

PBEWithMD5AndDES Cipher does not check for integrity first?

I am running FindBugs with findsecbugs plugin to scan java code for security issues. I am getting "Cipher With No Integrity" error for a Cipher function implemented with "PBEWithMD5AndDES". The legend ...
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1answer
127 views

AES-256 mode with per-block-key being a SHA-256 of SHA-256 of secret key, random public salt and block number. What's amiss?

Please criticize the (homebrew?) mode described below; to point out a single major defect/uncertainty or the link to (the analysis of) an equivalent construction is quite enough. Assume the ...
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1answer
198 views

What can be learned from the ciphertext of LibSodium's crypto_box_detached()?

LibSodium, (https://github.com/jedisct1/libsodium), has a function crypto_box_detached() which does authenticated encryption using the public key of the recipient ...
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1answer
57 views

Public-key encryption with associated data

In the symmetric-key world, we have authenticated encryption with associated data (AEAD). I'm looking for something similar, but for public-key encryption: public-key encryption with associated data (...
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1answer
28 views

Generally accepted algorithm for two-pass, misuse-resistant AEAD that is efficient in software

I would like to know what the standard is for two-pass, nonce-misuse-resistant AEAD that is efficient in software. Thus, AES-SIV is excluded; modes based on a stream cipher like ChaCha20 are ...
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1answer
35 views

NORX duplex padding

MonkeyDuplex constructions defined by Keccak authors has padding in every duplex block. Why only last duplex block is padded in NORX? Is it because NORX has domain separation, or simply because ...
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1answer
55 views

Is authentication length always a subset of encryption length?

Do in all the use cases, if I have to encrypt and authenticate, encrypt-then-authenticate or authenticate-then-encrypt, like in IPSEC, SSL or SSH or others, if I were to do these operations to a ...
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1answer
89 views

SpongeWrap without padding and frame bit

Assuming all inputs are same length as rate except last can be shorter. Is it necessary to pad every input (not just last) to sponge for authenticated encryption to be secure? Is this just, because ...
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1answer
1k views

How to supply the GCM authentication tag to the OpenSSL command line tools?

I'm using AES-256-GCM for authenticated encryption. In order to decrypt, the ruby OpenSSL library requires an auth_tag parameter (in addition to the key and iv). ...