Questions tagged [gcm]

The Galois Counter Mode, an authenticated encryption mode of operation for a block cipher.

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Can an AES-GCM be cracked if the key is known but the nonce isn't?

I'm kind of new in this field and I've been trying to learn it. I'm now facing an issue where I have a couple of packages encrypted with AES-128 GCM and I have the key that was used to encrypt these ...
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Line by line encrypted logging stored with iv/salt/iterations. How safe is it?

I'm building an encrypted logging application. Log entries are encrypted with AES-256-GCM, using password-derived keys with PBKDF2. The application must support log rotation, and I would like to make ...
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Can I use aes-gcm to authenticate a user based on his ability to decrypt a payload?

I'd like to authenticate my users without storing their password, even in a derived form with scrypt/pbkdf or other derivation methods. I'm exploring the idea of encrypting a random payload with AES ...
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Can I make fixed-length ciphertext with AES-256-GCM?

I have a question about AES-256-GCM encryption. Can I make a fixed-length encryption output? In my understanding, I cannot make a fixed-length ciphertext. To me, the fixed-length output is much more ...
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Does the size of data to be encrypted influence the security of Gmac?

In this link: Has GMAC mode a future outside GCM?, the last comment given by the user Demi, indicates that the larger the size of the text to be encrypted, the lower the security of the gmac. Why is ...
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Is it safe to generate GCM/GMAC intermediate tags?

I would like to use GCM/GMAC in next manner: abcd|Tag0|efgh|Tag1|ijkl|Tag2| ... |wxyz|TagN The nuance is each tag I gonna generate is not from its last block but ...
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Is this correct/incorrect password for file encryption scheme secure?

I'm writing an AES file encryption program, and I'd like to put in a way to tell whether or not the user has entered the correct password without decrypting the entire file and GCM telling me the tag ...
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AES-GCM - what are “Payload Length” and “AAD Length”

For the AES-GCM mode within many cryptomodules, their FIPS-validation certificates list the options: Payload Length: 504, 512, 1016, 1024 AAD Length: 0, 504, 512, 1016, 1024 For example in OpenSSL, "...
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What are the popular modes-of-operation (AES-GCM, AES-SIV, AES-GCM-SIV, etc.) geared for?

I'm interested in developing software capable of encrypting personal files (which will ultimately be backed up to the cloud) and have been doing my best to follow best practices. There are many forms ...
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How does AEAD guarantee authenticated encryption and plain AES does not?

This is a follow up to my earlier question. This is more out of curiosity in how AEAD (like CCM or GCM) works compared to encryption in other modes (like CBC or ECB). Suppose you have AES-256-CBC ...
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Security implications of not concatenating a 1 to the IV when using GCM

When using GCM, The padding string $0^{31}||1$ is appended to the IV. I know that this is done to avoid the repetition of $E_K(0^n)$ which is used as key for the GHash. But what would be the security ...
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How to encrypt files using AES256-GCM cipher under Linux? [closed]

I'm struggling to implement AES256-GCM on a Linux machine to encrypt files outgoing to another party. We're usually exchanging files using PKI, but this particular party insists on AES256-GCM and ...
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How does AES-GCM produce different ciphertexts, and how can the algorithm decrypt the values if they're random?

The title explains it. How does AES-GCM (or other modes for that matter) generate random ciphertexts per execution, and how does the algorithm decrypt a random value since the sender randomizes the ...
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Why can't AES-GCM be used in IKEv1 phase 1?

I was configuring a VPN on a firewall (fortigate) and realized that I could use AES-GCM for encryption in the IKEv1 phase 2 but not in the phase 1 and I was wondering why knowing that in IKEv2 we ...
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Why doesn't GMAC/GCM encrypt its authentication tag?

As most know, a duplicate nonce with GMAC/GCM allows key recovery attacks against GMAC itself and thus the ability to forge messages. This is because GMAC computes GHASH and then just XORs this with ...
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AEAD (for AES128-GCM): is it necessary to add a zero-length AAD?

In an implementation of AEAD_AES_128_GCM, if the AAD is defined as a "zero-length octet sequence", is it necessary to call the encryption code that adds an AAD at all? In particular, does an OpenSSL/...
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Using an AES-256-GCM key as a salt to SHA-256

Assume 256 bit keys are randomly generated and data is encrypted using AES-GCM-256 prior to being sent to a server. The goal is to enable the server to determine uniqueness of data it receives ...
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Nonce-misuse-resistance scheme applied after the fact to AES-GCM for defense in depth?

This is a follow-up to a previous question about encrypting IV/MAC results from AEAD ciphers. I have a system I'm working on that needs to use standard (NIST/FIPS) cryptography, at least for its ...
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Any benefit to encrypting IV and MAC in a mode like AES-GCM or ChaChaPoly?

Would there be any benefit to symmetrically encrypting the IV and MAC in an AEAD mode of operation? More specifically would this prevent someone from exploiting the accidental use of a duplicate IV ...
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Is the Java function AES/CBC/PKCS5Padding vulnerable to padding oracle?

I have an application that stores data on the devices. Currently AES/CBC/PKCS5Padding from javax.crypto.Cipher(see reference) is ...
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Is AES-GCM suitable for per chunk encryption?

I was looking through Google's encryption flow and noticed that they split each file into chunks and then encrypt each chunk individually with AES-GCM with its own key. Since AES-GCM starts to get ...
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Generating the Backup Exec AES-256 GCM key used to encrypt/decrypt LTO5 tape drive data

I've got an LTO5 tape that was backed up using Backup Exec (BE), which used hardware compression when writing to the tape. I've been given the passphrase that BE used to create the actual encryption ...
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Plain text size limits for AES-GCM mode at 2GB with Sun JCE implementation?

The Sun JCE implementation of GCM is hard coded to refuse to encode more than 2 Gb, through the function GaloisCounterMode.checkDataLength() that returns an error message : "SunJCE provider only ...
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AES-GCM cipher - Nonce vs IV

I am using a Python library called PyCryptodome, which offers the following API for AES-GCM ciphers: https://pycryptodome.readthedocs.io/en/latest/src/cipher/aes.html As you see, IV is not ...
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Does GCM improve the strenght of weak passwords?

If I am encrypting a file with GCM/AES256 with a weak key (say a sha256), does the fact that it takes time to brute force a long message improve my security? Example: I use the sha256 of "ARainyDay" ...
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Protocol Design for IoT devices having PSK using AES-GCM

Handshake: 1) Client To Server: "AES-GCM(Client_random_128bit,client_iv,psk),client_id,tag,client_iv" 2) Server To Client: "AES-GCM(Server_random_128bit,client_iv++,psk),tag ...
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Can a zero nonce be safely used with AES-GCM if the key is random and never used again?

I could generate a random nonce and prepend it to the ciphertext, but storage space is at a premium and the only constraint AES-GCM has on the nonce (if I'm reading correctly) is that the same nonce ...
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What is the Risk of Rotating Keys

This may be a difficult question So, $C_1$ = AES-GCM($k_1$, nonce, message) where nonce = HMAC(key,message). $C_2$ = AES-CBC($k_2$, iv, $C_1$). Now, a security breach occurs. The adversary obtains ...
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Can I Achieve Deterministic Encryption Using AES-GCM with Nonce = HMAC [ message ]

I would like to implement a deterministic encryption scheme within .NET. From the following post it is established using AES-SIV mode is appropriate. As AES-SIV mode is not implemented within the ...
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Why does the Signal protocol use AES/CBC instead of AES/GCM?

AES/GCM has obviously proved itself to be better than AES/CBC. Unless the key is re-used with the same initialization vector (see disadvantages of GCM). More information of its advantages against CBC ...
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Guessing the key in AES256-GCM? [duplicate]

I assume that my case is weird but I've the following information: IV: 0x263e or 0x3e26 Auth tag: 0x25 AES256-GCM encrypted payload: 0x4eec96df534ade4c013a AES256-GCM decrypted payload: ...
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AES-GCM cipher tag and IV size, while attempting to render encrypted ciphertext useless by removing them

I'm using AES in GCM mode of operation for encryption/decryption & authentication of segments of data in a file. The layout of each segment can be summerized by this diagram. Each segment is ...
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GCM optimisation using $M_0$ and $R$ tables - Calculation of $R$

I'm implementing GCM in C as a way to learn about it. In the paper titled as The Galois/Counter Mode of Operation (GCM) by McGrew and Viega on chapter 4.1, page 11, 12, they talk about the ...
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Using key derived using HKDF or NIST sp800-108 with AES-CCM/GCM

Is it safe to use keys derived using HKDF or NIST sp800-108 with AES-CCM/GCM ? The NIST SP800-108 and SP*00-56C spec says "To comply with this Recommendation, the derived keying material shall not be ...
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What should I use for consequent AES key derivation?

I am writing a small chat program to explore some methods and concepts in cryptography and currently I am using a shared AES key tunneled with RSA which upon further reading revealed many flaws both ...
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AES-256 GCM IV guidelines

If I use for example AES-256 (GCM), and my message is bigger than 256 bit (broken into smaller 256 bit blocks for encryption), should the IV change for every 256 bits of the message?
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How to handle the extra 12451 elements in Sophie-Germain Counter Mode?

In Sophie-Germain Counter Mode (SGCM), the $GF(2^{128})$ field multiplication of Galois Counter Mode (GCM) is replaced with normal multiplication $\bmod 2^{128}+12451$. Because the block size is 128 ...
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how does BearSSL's GCM modular reduction work?

BearSSL (in src/hash/ghash_ctmul.c) seems to be doing a modular reduction that I don't completely understand. Here's the code: ...
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How can you determine how long the MAC for GCM must be?

I want to use AES-GCM to encrypt 7 Byte data chunks. A 16 Byte MAC seems like overkill to me and the library I'm using gives me the option to make the MAC smaller. ...
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GCM with reversed poly

These slides talk about how GCM can be sped up if one uses $x^{128}+x^{127}+x^{126}+x^{121}+1$ as the reduction polynomial instead of $x^{128}+x^7+x^2+x^1+1$. When one is doing that one needs to ...
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With AES-GCM, may I use multiple tags per key?

In my implementation of AES-GCM, the key might change only once per minute. However, I wish to calculate a new tag every 6us, to reduce latency (since you have to buffer up a GCM "packet" before ...
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Implementations of GCM with 64-bit cipher

The paper The Galois/Counter Mode of Operation (GCM) describes mainly the 128-bit case, for use with 128-bit block ciphers such as AES. AES-GCM test vectors are available from NIST. The paper also ...
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how does AES GCM in SSH work?

I was looking at RFC5647: AES Galois Counter Mode for the Secure Shell Transport Layer Protocol and had some questions about section 7.1 "IV and Counter Management". Here's that section: ...
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Why doesn't the GCM spec use a more efficient multiplication algorithm?

NIST SP 800-38D § 6.3 Multiplication Operation on Blocks describes a multiplication algorithm that, in my testing, appears to be a good amount slower then algorithm 2.40 (arbitrary reduction ...
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GHASH with a finite field multiplication algorithm in reverse order

NIST SP 800-38D § 6.4 GHASH Function describes the GHASH algorithm thusly: Prerequisites: block $H$, the hash subkey. Input: bit string $X$ such that len($X$) = $128m$ for some positive ...
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modular reduction algorithm over $F_{2^m}$ doesn't seem to work when order of polynomial being reduced is small

I was considering algorithm 2.40 (arbitrary reduction polynomials) in the Guide to Elliptic Curve Cryptography and... it doesn't appear to work when the order of the polynomial you're trying to ...
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Are Authenticated Encryption ciphersuites supported in legacy TLS versions older than TLS 1.2?

I have read in a paper that Authenticated Encryption (by this I mean those that support GCM mode or ChaCha20 ciphers) are not supported in versions older than TLS 1.2? I could not confirm this as ...
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Does re-transmission really reduce security?

I am using AES with GCM and a colleague told me "Repeating a VCC with the same key and a different message reduces the security of the key." He did not have any additional detail to offer. What he ...
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CBC related TLS cipher suites to be disabled in the server side

I understand the TLS cipher suites using CBC mode are susceptible to timing attacks. From that understanding it seems that the cipher suites using GCM (CTR-based) are safe to use considering they don'...
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GCM decryption and clear text processing

When using GCM mode decryption, is it necessary to wait for the decryption to complete, (and thus being able to see if the integrity of cipher text is OK) before beginning processing the clear text ...

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