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Insecure private-key encryption

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2

$begingroup$

I am learning about crytography and the differences between the public and private keys encryption examples and I was wondering if it is possible to have a private key encryption scheme that is completely insecure? I have not been able to find what that could look like but I'm curious? Or is this not possible? Is the encryption scheme always secure with private keys?

encryption symmetric

share|improve this question

edited 20 mins ago

Ilmari Karonen

34.9k373138

asked 7 hours ago

droidnoob

$endgroup$

migrated from stackoverflow.com 2 hours ago

This question came from our site for professional and enthusiast programmers.

add a comment | 

2

$begingroup$

I am learning about crytography and the differences between the public and private keys encryption examples and I was wondering if it is possible to have a private key encryption scheme that is completely insecure? I have not been able to find what that could look like but I'm curious? Or is this not possible? Is the encryption scheme always secure with private keys?

encryption symmetric

share|improve this question

edited 20 mins ago

Ilmari Karonen

34.9k373138

asked 7 hours ago

droidnoob

$endgroup$

migrated from stackoverflow.com 2 hours ago

This question came from our site for professional and enthusiast programmers.

add a comment | 

$begingroup$

I am learning about crytography and the differences between the public and private keys encryption examples and I was wondering if it is possible to have a private key encryption scheme that is completely insecure? I have not been able to find what that could look like but I'm curious? Or is this not possible? Is the encryption scheme always secure with private keys?

encryption symmetric

share|improve this question

edited 20 mins ago

Ilmari Karonen

34.9k373138

asked 7 hours ago

droidnoob

$endgroup$

share|improve this question

edited 20 mins ago

Ilmari Karonen

34.9k373138

asked 7 hours ago

droidnoob

share|improve this question

edited 20 mins ago

Ilmari Karonen

34.9k373138

asked 7 hours ago

droidnoob

edited 20 mins ago

Ilmari Karonen

34.9k373138

edited 20 mins ago

Ilmari Karonen

34.9k373138

2 Answers
2

active

oldest

votes

3

$begingroup$

Any encryption scheme can be insecure if the key space is small enough.

For example, you could perform encryption with an 8 bit RSA key. For a key of that size, it's trivial to determine the private key given the public key.

share|improve this answer

answered 7 hours ago

dbushdbush

1965

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  would this be true even with a small message space? Or that wouldn't factor in?
  $endgroup$
  – droidnoob
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @droidnoob If your key is insecure nothing else matters. For example given an 8 bit RSA public key with exponent 3 modulus 187, it's trival to factor the modulus into 11 and 17, calculate lamda(187) = lcm(11-1,17-1) = 80, then calculate the private exponent d = 3^-1 mod 80 = 27.
  $endgroup$
  – dbush
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  thanks for reply. can I ask you one more? What if the key is completely secure and protected, would there be any way to have a completely secure key but insecure scheme?
  $endgroup$
  – droidnoob
  6 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  @droidnoob If you mean a poorly designed encryption algorithm, then yes.
  $endgroup$
  – dbush
  6 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  You could derive a subkey in your scheme that is much smaller than the input key, e.g. by hashing it and taking the leftmost bits. The original, large key could be completely secure - protected by the cryptographic hash - but you have again an encryption scheme with a small key space. Presto.
  $endgroup$
  – Maarten Bodewes♦
  5 hours ago
  

  
  
  
  

 | 
show 1 more comment

0

$begingroup$

What if the key is completely secure and protected, would there be any way to have a completely secure key but insecure scheme?

Yes, certainly. For example, consider the following encryption scheme:

• The key is a 256 bit (or, heck, 512 or 1024 bit if you want) string chosen uniformly at random by a cryptographically secure true random number generator, stored securely in a locked vault deep underground, with multiple armed guards watching the entrance 24/7.




• The encryption method doesn't use the key for anything, and instead encrypts the data using rot13.




• The decryption method is the same as the encryption method.

share|improve this answer

answered 10 mins ago

Ilmari KaronenIlmari Karonen

34.9k373138

$endgroup$

add a comment | 

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3

$begingroup$

Any encryption scheme can be insecure if the key space is small enough.

For example, you could perform encryption with an 8 bit RSA key. For a key of that size, it's trivial to determine the private key given the public key.

share|improve this answer

answered 7 hours ago

dbushdbush

1965

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  would this be true even with a small message space? Or that wouldn't factor in?
  $endgroup$
  – droidnoob
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @droidnoob If your key is insecure nothing else matters. For example given an 8 bit RSA public key with exponent 3 modulus 187, it's trival to factor the modulus into 11 and 17, calculate lamda(187) = lcm(11-1,17-1) = 80, then calculate the private exponent d = 3^-1 mod 80 = 27.
  $endgroup$
  – dbush
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  thanks for reply. can I ask you one more? What if the key is completely secure and protected, would there be any way to have a completely secure key but insecure scheme?
  $endgroup$
  – droidnoob
  6 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  @droidnoob If you mean a poorly designed encryption algorithm, then yes.
  $endgroup$
  – dbush
  6 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  You could derive a subkey in your scheme that is much smaller than the input key, e.g. by hashing it and taking the leftmost bits. The original, large key could be completely secure - protected by the cryptographic hash - but you have again an encryption scheme with a small key space. Presto.
  $endgroup$
  – Maarten Bodewes♦
  5 hours ago
  

  
  
  
  

 | 
show 1 more comment

3

$begingroup$

Any encryption scheme can be insecure if the key space is small enough.

For example, you could perform encryption with an 8 bit RSA key. For a key of that size, it's trivial to determine the private key given the public key.

share|improve this answer

answered 7 hours ago

dbushdbush

1965

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  would this be true even with a small message space? Or that wouldn't factor in?
  $endgroup$
  – droidnoob
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @droidnoob If your key is insecure nothing else matters. For example given an 8 bit RSA public key with exponent 3 modulus 187, it's trival to factor the modulus into 11 and 17, calculate lamda(187) = lcm(11-1,17-1) = 80, then calculate the private exponent d = 3^-1 mod 80 = 27.
  $endgroup$
  – dbush
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  thanks for reply. can I ask you one more? What if the key is completely secure and protected, would there be any way to have a completely secure key but insecure scheme?
  $endgroup$
  – droidnoob
  6 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  @droidnoob If you mean a poorly designed encryption algorithm, then yes.
  $endgroup$
  – dbush
  6 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  You could derive a subkey in your scheme that is much smaller than the input key, e.g. by hashing it and taking the leftmost bits. The original, large key could be completely secure - protected by the cryptographic hash - but you have again an encryption scheme with a small key space. Presto.
  $endgroup$
  – Maarten Bodewes♦
  5 hours ago
  

  
  
  
  

 | 
show 1 more comment

$begingroup$

Any encryption scheme can be insecure if the key space is small enough.

For example, you could perform encryption with an 8 bit RSA key. For a key of that size, it's trivial to determine the private key given the public key.

share|improve this answer

answered 7 hours ago

dbushdbush

1965

$endgroup$

share|improve this answer

answered 7 hours ago

dbushdbush

1965

answered 7 hours ago

dbushdbush

1965

answered 7 hours ago

dbushdbush

1965

0

$begingroup$

What if the key is completely secure and protected, would there be any way to have a completely secure key but insecure scheme?

Yes, certainly. For example, consider the following encryption scheme:

• The key is a 256 bit (or, heck, 512 or 1024 bit if you want) string chosen uniformly at random by a cryptographically secure true random number generator, stored securely in a locked vault deep underground, with multiple armed guards watching the entrance 24/7.




• The encryption method doesn't use the key for anything, and instead encrypts the data using rot13.




• The decryption method is the same as the encryption method.

share|improve this answer

answered 10 mins ago

Ilmari KaronenIlmari Karonen

34.9k373138

$endgroup$

add a comment | 

0

$begingroup$

What if the key is completely secure and protected, would there be any way to have a completely secure key but insecure scheme?

Yes, certainly. For example, consider the following encryption scheme:

• The key is a 256 bit (or, heck, 512 or 1024 bit if you want) string chosen uniformly at random by a cryptographically secure true random number generator, stored securely in a locked vault deep underground, with multiple armed guards watching the entrance 24/7.




• The encryption method doesn't use the key for anything, and instead encrypts the data using rot13.




• The decryption method is the same as the encryption method.

share|improve this answer

answered 10 mins ago

Ilmari KaronenIlmari Karonen

34.9k373138

$endgroup$

add a comment | 

$begingroup$

What if the key is completely secure and protected, would there be any way to have a completely secure key but insecure scheme?

Yes, certainly. For example, consider the following encryption scheme:

• The key is a 256 bit (or, heck, 512 or 1024 bit if you want) string chosen uniformly at random by a cryptographically secure true random number generator, stored securely in a locked vault deep underground, with multiple armed guards watching the entrance 24/7.




• The encryption method doesn't use the key for anything, and instead encrypts the data using rot13.




• The decryption method is the same as the encryption method.

share|improve this answer

answered 10 mins ago

Ilmari KaronenIlmari Karonen

34.9k373138

$endgroup$

share|improve this answer

answered 10 mins ago

Ilmari KaronenIlmari Karonen

34.9k373138

answered 10 mins ago

Ilmari KaronenIlmari Karonen

34.9k373138

answered 10 mins ago

Ilmari KaronenIlmari Karonen

34.9k373138