Length extension attack. Everything you need to know about hash length extension attacks

Discussion in '2019' started by Faerg , Saturday, March 19, 2022 7:32:22 AM.

  1. Gardagor

    Gardagor

    Messages:
    95
    Likes Received:
    20
    Trophy Points:
    10
    That problem of mine was the point - you have to change the appended length as well. Client's calculation So, how do we calculate the hash of the data shown above without actually having access to secret? This flexibility does not indicate an exploit in the message format, because the message format was never designed to be cryptographically secure in the first place, without the signature algorithm to help it. The value of that block of data can be calculated in two ways:. When we creating the perfect message hash, we thus need to make sure we have:. Reply You, sir, are a rockstar. HoweverI can imagine myself doing it.
     
  2. Arashiran

    Arashiran

    Messages:
    686
    Likes Received:
    20
    Trophy Points:
    6
    In cryptography and computer security, a length extension attack is a type of attack where an attacker can use Hash(message1) and the length of message1 to.This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
    Length extension attack. Subscribe to RSS
     
  3. Bak

    Bak

    Messages:
    663
    Likes Received:
    7
    Trophy Points:
    3
    In cryptography and computer security, a length extension attack is a type of attack where an attacker can use Hash and the length of message₁ to calculate Hash for an attacker-controlled message₂, without needing to know the content of message₁.Save my name, email, and website in this browser for the next time I comment.
     
  4. Arajora

    Arajora

    Messages:
    724
    Likes Received:
    12
    Trophy Points:
    7
    An application is susceptible to a hash length extension attack if it prepends a secret value to a string, hashes it with a vulnerable algorithm.Why is it so difficult?
     
  5. Nataxe

    Nataxe

    Messages:
    704
    Likes Received:
    30
    Trophy Points:
    5
    Basically the vulnerable algorithms generate the hashes by firstly hashing a block of data, and then, from the previously created hash (state).The one-way function f will generally compress the data and produce fewer bits out than are fed in.
    Length extension attack.
     
  6. Zologor

    Zologor

    Messages:
    130
    Likes Received:
    16
    Trophy Points:
    1
    Length Extension Attacks, The Simple Explanation Cryptographic hash functions, such as MD5, SHA1, SHA2, etc., are based on a construct known.The signature used here is a MACsigned with a key not known to the attacker.
    Length extension attack.
     
  7. Tesida

    Tesida

    Messages:
    518
    Likes Received:
    14
    Trophy Points:
    7
    SHA-1 processes data by bit blocks (64 bytes). For a given input message m, it first appends some bits (at least 65, at most ) so.What good can it do to the attacker?
     
  8. Mazudal

    Mazudal

    Messages:
    411
    Likes Received:
    20
    Trophy Points:
    6
    portalnews.top › marcelo › length-extension.The B they talk about stands for block size but lets ignore the padding stuff to keep it simpler and see what we get.
     
  9. Mikadal

    Mikadal

    Messages:
    426
    Likes Received:
    10
    Trophy Points:
    5
    The key idea behind the Length Extension Attack is that the output of the hash function corresponds to its internal state when it finishes processing the input.After all of the input has been processed, the hash digest is generated by outputting the internal state of the function.
     
  10. Kelar

    Kelar

    Messages:
    299
    Likes Received:
    31
    Trophy Points:
    1
    The MD construct has many weaknesses, and one of the most serious is the length extension attack. With this an adversary (Eve) can take a hash for an.The derived hash function starts with an internal state of size M and takes an input of variable size that is broken into multiple blocks of size N.
     
  11. Meztigami

    Meztigami

    Messages:
    621
    Likes Received:
    13
    Trophy Points:
    3
    This week I spent a little bit of time working on Hash Length Extensions. HLE is a technique that allows an attacker to abuse poorly constructed authentication.The difference is, we didn't use secret at all!
     
  12. Zurisar

    Zurisar

    Messages:
    335
    Likes Received:
    24
    Trophy Points:
    5
    The padded message m p is then split into successive bit blocks, which are processed one after the other.
     
  13. Moramar

    Moramar

    Messages:
    50
    Likes Received:
    20
    Trophy Points:
    6
    forum? The difference is, we didn't use secret at all!
     
  14. Gakinos

    Gakinos

    Messages:
    932
    Likes Received:
    23
    Trophy Points:
    0
    All right, so the server is going to be checking the data we send against the signature 6eeacefcdadee.
     
  15. Brabar

    Brabar

    Messages:
    681
    Likes Received:
    24
    Trophy Points:
    0
    This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
     
  16. Ter

    Ter

    Messages:
    825
    Likes Received:
    22
    Trophy Points:
    7
    Very good and nicely written.
     
  17. Nisar

    Nisar

    Messages:
    42
    Likes Received:
    9
    Trophy Points:
    3
    This can be given multiple times if you want to try multiple signatures.
     
  18. Zolorr

    Zolorr

    Messages:
    760
    Likes Received:
    12
    Trophy Points:
    5
    Reply Rob, Does this attack and your tool works if hashing is as follow: md5 data.
    Length extension attack.
     
  19. Meztigore

    Meztigore

    Messages:
    912
    Likes Received:
    16
    Trophy Points:
    2
    The compression function is continuosly applied to each block of size N and the internal state of size M, resulting in a new internal state at each step.
     
  20. Tugar

    Tugar

    Messages:
    156
    Likes Received:
    11
    Trophy Points:
    2
    Notice that we need only the length of M1, not its contents.
     
  21. Kigarr

    Kigarr

    Messages:
    128
    Likes Received:
    14
    Trophy Points:
    1
    The padded message m p is then split into successive bit blocks, which are processed one after the other.
     
  22. Voodoojind

    Voodoojind

    Messages:
    220
    Likes Received:
    6
    Trophy Points:
    7
    Put together, it looks like this:.
     
  23. Kedal

    Kedal

    Messages:
    436
    Likes Received:
    14
    Trophy Points:
    1
    These 8 last bytes are used to represent the size of the message in bits.
     
  24. Kigazshura

    Kigazshura

    Messages:
    908
    Likes Received:
    5
    Trophy Points:
    6
    Do you mean that i feed the SHA-1 with h m p z?
     
  25. Teramar

    Teramar

    Messages:
    355
    Likes Received:
    21
    Trophy Points:
    5
    Cryptography Stack Exchange works best with JavaScript enabled.
     
  26. Meztikora

    Meztikora

    Messages:
    836
    Likes Received:
    25
    Trophy Points:
    6
    In order to sign this new message, typically the attacker would need to know the key the message was signed with, and generate a new signature by generating a new MAC.
     
  27. Nakora

    Nakora

    Messages:
    679
    Likes Received:
    21
    Trophy Points:
    4
    If you can't avoid it, then use HMAC instead of trying to do it yourself.
     
  28. Mishakar

    Mishakar

    Messages:
    654
    Likes Received:
    10
    Trophy Points:
    5
    The endianness of the length field is also important.
     
  29. Madal

    Madal

    Messages:
    731
    Likes Received:
    29
    Trophy Points:
    0
    In this request, the original key's length was 14 bytes, which could be determined by trying forged requests with various assumed lengths, and checking which length results in a request that the server accepts as valid.
     
  30. Moogusho

    Moogusho

    Messages:
    790
    Likes Received:
    16
    Trophy Points:
    1
    The vulnerable hashing functions work by taking the input message, and using it to transform an internal state.
     
  31. Moshakar

    Moshakar

    Messages:
    397
    Likes Received:
    30
    Trophy Points:
    2
    I have to account for padding.
     
  32. Yozshuk

    Yozshuk

    Messages:
    527
    Likes Received:
    27
    Trophy Points:
    2
    If I knew mI could build the larger message.
     
  33. Arashinos

    Arashinos

    Messages:
    860
    Likes Received:
    17
    Trophy Points:
    4
    Reply Nice tool and write-up, thanks!
     
  34. Babar

    Babar

    Messages:
    120
    Likes Received:
    15
    Trophy Points:
    2
    Note that we are resuming to an internal state where the block above was already processed, meaning that we don't need to know the secret to produce the new MAC.
     
  35. Akinogul

    Akinogul

    Messages:
    796
    Likes Received:
    7
    Trophy Points:
    0
    Is it, ?Forum Length extension attack
     
  36. Doujinn

    Doujinn

    Messages:
    609
    Likes Received:
    15
    Trophy Points:
    5
    Thanks in advance!
     
  37. Felabar

    Felabar

    Messages:
    990
    Likes Received:
    5
    Trophy Points:
    5
    This scheme breaks in the presence of the length-extension attack: if I, as an attacker, see a MAC for a message dthen I can compute the MAC for a message d' which extends d -- and I can do that without knowing k d so, in particular, without knowing the key.
     
  38. Bazil

    Bazil

    Messages:
    473
    Likes Received:
    17
    Trophy Points:
    5
    Let's see how.
     
  39. Kigak

    Kigak

    Messages:
    750
    Likes Received:
    17
    Trophy Points:
    0
    The signature used here is a MACsigned with a key not known to the attacker.
     
  40. Tujind

    Tujind

    Messages:
    520
    Likes Received:
    18
    Trophy Points:
    1
    SHA-3, which is based on a Keccac sponge, is not vulnerable to this.Forum Length extension attack
     
  41. Douzshura

    Douzshura

    Messages:
    907
    Likes Received:
    22
    Trophy Points:
    7
    We'll consider SHA as the hash function.
     
  42. Nigor

    Nigor

    Messages:
    951
    Likes Received:
    18
    Trophy Points:
    1
    Moving on
     
  43. Yozshuktilar

    Yozshuktilar

    Messages:
    550
    Likes Received:
    28
    Trophy Points:
    6
    But not now
     

Link Thread

  • Formica discontinued colors

    Nikolkis , Thursday, March 24, 2022 5:17:34 PM
    Replies:
    20
    Views:
    9783
    Mirisar
    Saturday, March 26, 2022 8:29:57 PM
  • Shannon entropy matlab

    Zolozragore , Wednesday, March 30, 2022 6:48:48 AM
    Replies:
    9
    Views:
    1332
    Shaktirn
    Wednesday, April 6, 2022 10:29:18 PM
  • Ultra sigma linux

    Mausho , Monday, March 28, 2022 2:46:25 PM
    Replies:
    23
    Views:
    2275
    Kajicage
    Saturday, April 2, 2022 8:32:14 PM
  • Termios rs485

    Megor , Thursday, April 7, 2022 4:54:28 AM
    Replies:
    10
    Views:
    2875
    Nira
    Monday, April 4, 2022 10:10:28 AM