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Questions tagged [padding-oracle]

A side-channel attack on implementations of encryption modes that use padding (e.g. ECB, CBC) that uses information leaked during decryption of tampered ciphertext values to derive information about the plaintext.

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The 9 lives of Bleichenbacher's CAT, it puts another scratch again

Bleichenbacher demonstrated a padding oracle attack against RSA implementations that follow the PKCS #1 v1.5. Through the years, there are various mitigation techniques developed as OAEP and limiting ...
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1answer
235 views

Is every block padded with AES?

I am looking at a tutorial on the Oracle Padding Attack, and I wondered, how do you find the rest of the blocks(not the last one), if there's only padding on 1 block? Am I not understanding padding ...
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3answers
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Padding Oracle: Why should padding be 0x01?

I just finished reading about padding oracle attacks at https://blog.skullsecurity.org/2013/a-padding-oracle-example, and it blew my mind. I think I understand almost all of it, but I do not ...
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Having trouble with padding oracle attack (in AES-256-CBC)

I have problems in understanding padding oracle attack and testing it on a given ciphertext on a server. The ciphertext is encoded with AES-256-CBC and padding is used such that the encoded message ...
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241 views

How can you change this message which is in block cipher AES-256 in CBC?

Given is the secret message encrypted with AES-256 in CBC mode 5a04ec902686fb05a6b7a338b6e07760 14c4e6965fc2ed2cd358754494aceffa The first 16 Byte is the initial ...
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51 views

Security implications of plaintext-padding in an AEAD-scheme

Let's say I have a secure AEAD-scheme like ChaCha20/HMAC and my encrypted blobs need to match a fixed size: Is it OK to apply some padding to my plaintext to match the block-size? Can I use any ...
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1answer
717 views

How to perform the padding oracle attack on AES CBC?

Assume I am the attacker. I want to break the plaintext by performing the padding oracle attack on AES CBC mode. I know the following information: ...
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1answer
598 views

Why was Vaudenay's original padding oracle attack not exploitable on TLS 1.0?

Reading Password Interception in a SSL/TLS Channel that was released in 2003: At Eurocrypt’02, Vaudenay presented vulnerabilities in padding schemes used for block ciphers in CBC mode. He used a ...
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394 views

Encrypting any text without key after padding oracle attack in CBC mode

Suppose the decryption program is already built. Now I want to encrypt an arbitrary plain text given the IV and the decryption program (no key). From the formulas, we have $$Dec(C_i)\oplus C_{i-1}=P_i$...
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226 views

Security effects of the seed's length in OAEP

In the OAEP scheme for asymetric encryption padding a random seed is used, whose length can be chosen. The paper which introduced OAEP in 1994 just states, that the seed's length $k_0$ should be ...
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1answer
180 views

CBC Padding Oracle in SSL3. Why only in SSL3 not in TLS1,TLS1.1, etc

I read about PODDLE attack which downgrades the TLS version to SSL 3.0 to exploit CBC padding oracle attack. I looked at the specs for TLS 1.1 And found CBC is still used in its ciphersuites. Why is ...
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342 views

Zero padded signatures in the Bleichenbacher attack

I'm studying this attack and i have some doubts about it; let me explain with an example. Here is my decoded signature: 00 01 FF .. FF .. 00 ASN1 HASH I forge a ...
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135 views

Weird size of data transmitted in SSLv3

Note - I know SSLv3 is dangerous but that is why I am using it to do demo of POODLE attack using server and client written in python. So the question is I am using "ECDHE-RSA-AES128-SHA" cipher for ...
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1answer
216 views

Cracking lowest plaintext bit in Padding oracle attack with PKCS#5

I have been working on a C implementation of padding oracle attack on a block encryption algorithm using CBC mode of operation. I understand the concept fine but I can't seem to find an answer to the ...
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2answers
1k views

Padding oracle attack, encrypting your own message

My understanding of the encryption attack on a padding oracle is that the attacker has a set of $P_i$'s and $\operatorname{Dec}(C_i)$'s I understand that by back calculating the attacker can find out ...
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2answers
630 views

How does a Padding Oracle Attack work in practice?

I have understood how the padding oracle attack works in theory. Now, I am trying to visualize it in a real scenario. Can someone please give a real scenario in which an attacker can insert himself ...
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1answer
570 views

Attack RSA with PKCSv1.5 padding

I was reading an article about breaking RSA with PKCSv1.5 padding (http://mslc.ctf.su/wp/google-ctf-spotted-wobbegong-crypto-100/). It says that while retrieving the message we multiply by the ...
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2answers
210 views

Clarification on the origin of `01` in this oracle padding attack?

I have found what I believe to be a straightforward explanation of the oracle padding attack here: http://robertheaton.com/2013/07/29/padding-oracle-attack/ I am however getting confused by something ...
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2answers
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Layman's description of the padding oracle attack

I understand that the MAC-then-encrypt approach is susceptible to several attacks including the so called padding oracle attack. I understand that in this attack the attacker modifies the padding and ...
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2answers
215 views

Is this approach able to protect against padding oracle attacks?

I know that a protection against the padding oracle attack is to encrypt-then-mac. This is to avoid trying to decrypt a modified ciphertext, and leak information about padding errors. Suppose that we ...
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0answers
473 views

Attacking AES-CTR mode with known prefix [duplicate]

My question is the following: Consider a 128-bit AES-CTR mode encryption on a plain-text $m$ . The structure of $m$ is constant. First comes a string, let's say : "JustSomeText\" followed by 5 ...
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1answer
137 views

Will changing the RSA Padding in OpenSSL cause issues?

I'm currently looking at changing the padding type from one of the Oracle Padding attacks to a secure one. Would this break data already encrypted using the old method?
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176 views

Block cipher detect padding behaviour

Suppose i have a crypto provider, i.e: i give that provider some plaintext bytes and get the encrypted result. I don't know the used encryption method, but i know ...
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1answer
263 views

How does padding oracle attack work with bytes larger than possible length?

I am trying to understand how the POODLE attack would actually be implemented. In the original security advisory from Möller, Duong and Kotowicz [POODLE 14] the following example is presented: ...
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3answers
192 views

Does a padding oracle have the encryption key? Where in real life do I see such an oracle?

So after some searching, I kinda know the attack procedure of altering bit by bit. But I'm still confused how this is possible. If I understand it correctly, the attacker never has the key, or tries ...
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2answers
469 views

Creating own ciphertext after a padding oracle attack?

I've written a script that breaks a cipher text based on a padding oracle for an assignment, but was wondering how I would continue on to create my own cipher text with any plain text I desired? ...
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2answers
5k views

How to verify the integrity of RSA encrypted messages?

I need to encrypt messages using PublicKeyCrypto and send it to the server, where the message should be decrypted. I'm aware of the Padding Oracle Attack and want to apply a server side integrity ...
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1answer
769 views

Is RSA vulnerable to the padding oracle attack?

I know that AES in combination with CBC mode is vulnerable against the Padding Oracle Attack. RSA also uses some kind of padding, hence can this attack be apply to RSA encrypted messages too?
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3answers
297 views

Why not put MAC in fixed position and cover padding for MAC-then-encrypt?

The biggest problem with using MtE with a mode where it's known to be secure (CBC) is with the padding, where you can't retrieve the authentication until you know where it is by looking at the padding ...
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1answer
274 views

poodle padding multiple blocks?

I'm quite new to the topic and read a bit about poodle and padding oracle. I quite understand the "regular" padding oracle attack, substituting the last byte of block(n-1) to determine the last byte ...
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1answer
314 views

How to make PKCS conformation oracle for trying Bleichenbacher’s RSA attack?

I was trying to understand Bleichenbacher’s CCA attack and thought of work it out in python. Can some one throw some light on the the logic behind the oracle used to check PKCS conformation? Will a ...
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2answers
739 views

Why is this a fix to Bleichenbacher's attack?

Looking at this excellent explaination of the attack, I have one additional question: It says that: ""To prevent this attack, SSL servers do not inform the client about padding woes. If decryption ...
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174 views

CBC-R when IV unknown

I've read the CBC-R description from Rizzo & Duong but am having trouble understanding the sequence of steps that would be taken when the IV is unknown and is not included with the ciphertext. ...
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2answers
313 views

Why verify padding at all?

Whenever a ciphertext is decrypted using a block-cypher, we need to remove the padding. There are different ways to add padding, but they usually set the last byte of the last block to the number of ...
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1answer
316 views

Bit padding instead of PKCS#5 padding

Padding oracle attacks are a huge nuisance when using CBC mode encryption without authentication. Wouldn't all those padding oracle attacks be avoided if we'd just use bit padding instead? Or is does ...
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3answers
5k views

Modes of operation that allow padding oracle attacks

It seems to me that padding oracle attacks are mainly a concern for users of CBC mode encryption. Question: are any other modes of operation vulnerable to padding oracle attacks? And if so, why? ...
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0answers
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Defending hybrid encryption schemes against padding oracle attacks

I intend to use a generic integrated/hybrid encryption scheme for transmitting information between a client and a server. Key encapsulation: a 128-bit symmetric key is generated and asymmetrically ...
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1answer
3k views

Bleichenbacher 1998 “Million message attack” on RSA

I have been reading Bleichenbacher's 1998 paper on a forged message attack on RSA. The paper assumes access to an Oracle that takes a ciphertext $c$ and will check the decrypted text for valid PKCS #1 ...
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1answer
727 views

Is it safe to use GZIP to avoid padding related attacks

I am designing a library that supports encrypting some in-memory data using AES in CBC mode. Now I need a padding but it seemed to me that Apple's CommonCrypto library and OpenSSL have different ...
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1answer
252 views

Security of (cryptographic) padding compared to other methods for blockcompletion for block ciphers

As said in the heading, I want to know how the security of different padding methods, e.g. ANSI X.923, ISO 10126 and PKCS7, is compared to other methods to reach the needed block size, like ciphertext ...
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2answers
11k views

Using the same secret key for encryption and authentication in a Encrypt-then-MAC scheme

Is it a weakness to use a single shared secret for protecting messages using a Encrypt-then-MAC scheme? Assuming a system is using AES-256-CBC and a SHA1-HMAC and the same secret key for both ...
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1answer
359 views

How to use HMAC for large ciphertexts over TLS

HMAC used to secure chosen cipher-text attacks. if we are encrypting a large file (video) and sending it over TLS for decryption, how server can check MAC for ciphertext when we didn't sent whole of ...
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1answer
2k views

Extract private RSA key from USB cryptographic token using Bardou et al. attack (variant of “million message attack”)

There is a side channel attack on tamper-resistant USB cryptographic tokens using padding-oracle, described by Bardou, Focardi, Kawamoto, Simionato, Steel and Tsay, titled "Efficient padding oracle ...
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1answer
707 views

Understanding padding oracles - is an attack plausible in my scenario?

I have a scheme that, long story short, uses AES in CBC mode to encrypt third-party credentials for user accounts with a password-derived key. It's been mentioned that the use of CBC mode is a ...
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2answers
171 views

What is an easy method of proving that a cryptographic oracle attack is possible?

Lets say an application is using CBC mode without authentication. The application is generating cipher text. This cipher text can be manipulated by the attacker and then transmitted back to the ...
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1answer
2k views

Shortcuts / practicality of brute forcing block cipher (AES) + ECB with known plaintext

I know the plaintext (26 bytes long) and cryptotext of block cipher (suspected to be AES) in ECB mode. I can generate hundreds or thousands of such samples, but the samples are not arbitrary. What are ...
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13k views

How does a padding oracle attack work?

I am unsure of how a padding oracle attack works. What I am not getting is how changing one bit at one time allows one to exploit(get keys) ASP.NET machines. Can anyone explain this?