Why does BitLocker not use RSA? Announcing the arrival of Valued Associate #679: Cesar...

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Why does BitLocker not use RSA?



Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 23, 2019 at 23:30 UTC (7:30pm US/Eastern)Should RSA public exponent be only in {3, 5, 17, 257 or 65537} due to security considerations?Securely read encryption key from NVRAM of TPM 1.2Methods of cold boot attacks in the wildClarification of RSA Key Exchange (TLS 1.2) and AES for On-Going Message ExcahngeShould I really salt in a RSA/AES hybrid connection?Anniversary Update with Bitlocker Reboot without Encryption KeyIs it possible to extract secrets from a TPM without knowing the PIN?Security of TPM 1.2 for providing tamper-evidence against firmware modificationHow does full memory encryption in newer processes protect against DMA attacks?How does Bitlocker + TPM prevent me seeing the HDD contents with another OS?Is GPG's AES encryption that much stronger than its RSA headers?





.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ margin-bottom:0;
}







5















If I do not understand wrong from this post and Wikipedia page of the BitLocker and TPM, by default, BitLocker uses symmetric cryptography like AES. However, TPM is capable of performing RSA encryption.
Given that, the RSA key is stored in the TPM, why BitLocker does not use the asymmetric encryption (i.e., RSA)? By using such encryption technique, we might be able to defend against the cold boot attack or sniffing on LPC bus.










share|improve this question









New contributor




user3862410 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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  • 8





    How would using asymmetric encryption even help? Unless you never intend to write any data to the disk, you would need to have both sides of the key in memory in order to use the disk anyway. (I suppose there are special cases where you'd want a disk anyone can read but with strong authentication of its content -- but even there encrypting each block separately with an asymmetric primitive would not be the solution of choice).

    – Henning Makholm
    15 hours ago




















5















If I do not understand wrong from this post and Wikipedia page of the BitLocker and TPM, by default, BitLocker uses symmetric cryptography like AES. However, TPM is capable of performing RSA encryption.
Given that, the RSA key is stored in the TPM, why BitLocker does not use the asymmetric encryption (i.e., RSA)? By using such encryption technique, we might be able to defend against the cold boot attack or sniffing on LPC bus.










share|improve this question









New contributor




user3862410 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
















  • 8





    How would using asymmetric encryption even help? Unless you never intend to write any data to the disk, you would need to have both sides of the key in memory in order to use the disk anyway. (I suppose there are special cases where you'd want a disk anyone can read but with strong authentication of its content -- but even there encrypting each block separately with an asymmetric primitive would not be the solution of choice).

    – Henning Makholm
    15 hours ago
















5












5








5


1






If I do not understand wrong from this post and Wikipedia page of the BitLocker and TPM, by default, BitLocker uses symmetric cryptography like AES. However, TPM is capable of performing RSA encryption.
Given that, the RSA key is stored in the TPM, why BitLocker does not use the asymmetric encryption (i.e., RSA)? By using such encryption technique, we might be able to defend against the cold boot attack or sniffing on LPC bus.










share|improve this question









New contributor




user3862410 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.












If I do not understand wrong from this post and Wikipedia page of the BitLocker and TPM, by default, BitLocker uses symmetric cryptography like AES. However, TPM is capable of performing RSA encryption.
Given that, the RSA key is stored in the TPM, why BitLocker does not use the asymmetric encryption (i.e., RSA)? By using such encryption technique, we might be able to defend against the cold boot attack or sniffing on LPC bus.







aes rsa tpm bitlocker cold-boot-attack






share|improve this question









New contributor




user3862410 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











share|improve this question









New contributor




user3862410 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









share|improve this question




share|improve this question








edited 1 hour ago









chrki

1053




1053






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asked 22 hours ago









user3862410user3862410

315




315




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New contributor





user3862410 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






user3862410 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.








  • 8





    How would using asymmetric encryption even help? Unless you never intend to write any data to the disk, you would need to have both sides of the key in memory in order to use the disk anyway. (I suppose there are special cases where you'd want a disk anyone can read but with strong authentication of its content -- but even there encrypting each block separately with an asymmetric primitive would not be the solution of choice).

    – Henning Makholm
    15 hours ago
















  • 8





    How would using asymmetric encryption even help? Unless you never intend to write any data to the disk, you would need to have both sides of the key in memory in order to use the disk anyway. (I suppose there are special cases where you'd want a disk anyone can read but with strong authentication of its content -- but even there encrypting each block separately with an asymmetric primitive would not be the solution of choice).

    – Henning Makholm
    15 hours ago










8




8





How would using asymmetric encryption even help? Unless you never intend to write any data to the disk, you would need to have both sides of the key in memory in order to use the disk anyway. (I suppose there are special cases where you'd want a disk anyone can read but with strong authentication of its content -- but even there encrypting each block separately with an asymmetric primitive would not be the solution of choice).

– Henning Makholm
15 hours ago







How would using asymmetric encryption even help? Unless you never intend to write any data to the disk, you would need to have both sides of the key in memory in order to use the disk anyway. (I suppose there are special cases where you'd want a disk anyone can read but with strong authentication of its content -- but even there encrypting each block separately with an asymmetric primitive would not be the solution of choice).

– Henning Makholm
15 hours ago












3 Answers
3






active

oldest

votes


















9














Asymmetric encryption is vastly inferior to symmetric encryption. That is, in all respects, except one -- being asymmetric. When that property is needed, there's no way around it, obviously.



Asymmetric encryption is much slower. It is much more susceptible to showing recognizable patterns of some kind given non-random input. You need much larger key sizes to provide an adequate level of protection, and the system is much more vulnerable in general with current and future technology (reasonably-sized quantum computers will basically mean instant death for RSA, but AES is pretty much "yeah, so what" in that respect).



That's the reason why asymmetric encryption is almost never used to encrypt bulk data.



Nothing prevents you from encrypting a terabyte of data with RSA using 2048 bit chunks, much like you encrypt a terabyte with AES in 128 bit chunks. Only just, it doesn't make sense to do that because it is several thousand times slower, and at the same time is much more insecure.






share|improve this answer
























  • vastly inferior? Compare the expand of cryptography after invention on Asymmetric Cryptography.

    – kelalaka
    13 hours ago











  • @kelalaka For communication.

    – wizzwizz4
    4 hours ago



















10














Asymmetric encryption like RSA is limited in that you can only use it to encrypt data the size of the key. With a 2048 bit key, you can only encrypt 2048 bits of information. For this reason RSA is unsuitable for bulk encryption like disks - and even for small files like email messages.



This is why almost all uses of asymmetric encryption involve "hybrid encryption". RSA is used to encrypt the key for a symmetric algorithm like AES, and AES is used to encrypt the bulk data. PGP is an example of a hybrid encryption application.





Correction - as @HenningMakholm points out in the comments, it isn't that asymmetric can't be chained to handle larger blocks of data the way symmetric algorithms do, it's that doing so is impractical from a performance point of view. The end effect is the same, but the mechanism is different.






share|improve this answer





















  • 8





    And AES can only encrypt 128 bits of information. There are well-known solutions to using AES for larger amounts of data, and some of them could be applied with RSA as the underlying primitive instead of AES. Performance would be dismal, though, which is the real reason why this is not done.

    – Henning Makholm
    15 hours ago






  • 2





    I'm not sure why this answer has so many upvotes, it's flat-out wrong. That's not the difference between RSA and AES, it's the difference between block-ciphers (including both RSA and AES) and stream ciphers. And it's not even a big deal, since you can easily turn any block cipher into a stream cipher using the various modes.

    – BlueRaja - Danny Pflughoeft
    4 hours ago





















3














The coldboot attack can be performed on any encryption scheme as long as the keys are residing on the memory. For full-disk encryption (FDE) with symmetric algorithms like AES , you will need to take out the key from the TPM, where you will be applicable to coldboot attack.



Though the TPM is capable of RSA encryption and decryptions, for FDE the RSA has problems, in short the speed;




  1. RSA must use AOEP scheme to be secure which reduces the message size.

  2. To speed up the public key encryption the public key is selected as 3, 5, ... However, the decryption to access one block will be much more slower even you use CRT to gain 4x speed.

  3. Even the TPM can perform RSA encryption on the chip, it will be much slower for Full Disk Encryption (FDE).


Therefore, TPM based FDEs use TPM as a key storage.






share|improve this answer
























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    3 Answers
    3






    active

    oldest

    votes








    3 Answers
    3






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    9














    Asymmetric encryption is vastly inferior to symmetric encryption. That is, in all respects, except one -- being asymmetric. When that property is needed, there's no way around it, obviously.



    Asymmetric encryption is much slower. It is much more susceptible to showing recognizable patterns of some kind given non-random input. You need much larger key sizes to provide an adequate level of protection, and the system is much more vulnerable in general with current and future technology (reasonably-sized quantum computers will basically mean instant death for RSA, but AES is pretty much "yeah, so what" in that respect).



    That's the reason why asymmetric encryption is almost never used to encrypt bulk data.



    Nothing prevents you from encrypting a terabyte of data with RSA using 2048 bit chunks, much like you encrypt a terabyte with AES in 128 bit chunks. Only just, it doesn't make sense to do that because it is several thousand times slower, and at the same time is much more insecure.






    share|improve this answer
























    • vastly inferior? Compare the expand of cryptography after invention on Asymmetric Cryptography.

      – kelalaka
      13 hours ago











    • @kelalaka For communication.

      – wizzwizz4
      4 hours ago
















    9














    Asymmetric encryption is vastly inferior to symmetric encryption. That is, in all respects, except one -- being asymmetric. When that property is needed, there's no way around it, obviously.



    Asymmetric encryption is much slower. It is much more susceptible to showing recognizable patterns of some kind given non-random input. You need much larger key sizes to provide an adequate level of protection, and the system is much more vulnerable in general with current and future technology (reasonably-sized quantum computers will basically mean instant death for RSA, but AES is pretty much "yeah, so what" in that respect).



    That's the reason why asymmetric encryption is almost never used to encrypt bulk data.



    Nothing prevents you from encrypting a terabyte of data with RSA using 2048 bit chunks, much like you encrypt a terabyte with AES in 128 bit chunks. Only just, it doesn't make sense to do that because it is several thousand times slower, and at the same time is much more insecure.






    share|improve this answer
























    • vastly inferior? Compare the expand of cryptography after invention on Asymmetric Cryptography.

      – kelalaka
      13 hours ago











    • @kelalaka For communication.

      – wizzwizz4
      4 hours ago














    9












    9








    9







    Asymmetric encryption is vastly inferior to symmetric encryption. That is, in all respects, except one -- being asymmetric. When that property is needed, there's no way around it, obviously.



    Asymmetric encryption is much slower. It is much more susceptible to showing recognizable patterns of some kind given non-random input. You need much larger key sizes to provide an adequate level of protection, and the system is much more vulnerable in general with current and future technology (reasonably-sized quantum computers will basically mean instant death for RSA, but AES is pretty much "yeah, so what" in that respect).



    That's the reason why asymmetric encryption is almost never used to encrypt bulk data.



    Nothing prevents you from encrypting a terabyte of data with RSA using 2048 bit chunks, much like you encrypt a terabyte with AES in 128 bit chunks. Only just, it doesn't make sense to do that because it is several thousand times slower, and at the same time is much more insecure.






    share|improve this answer













    Asymmetric encryption is vastly inferior to symmetric encryption. That is, in all respects, except one -- being asymmetric. When that property is needed, there's no way around it, obviously.



    Asymmetric encryption is much slower. It is much more susceptible to showing recognizable patterns of some kind given non-random input. You need much larger key sizes to provide an adequate level of protection, and the system is much more vulnerable in general with current and future technology (reasonably-sized quantum computers will basically mean instant death for RSA, but AES is pretty much "yeah, so what" in that respect).



    That's the reason why asymmetric encryption is almost never used to encrypt bulk data.



    Nothing prevents you from encrypting a terabyte of data with RSA using 2048 bit chunks, much like you encrypt a terabyte with AES in 128 bit chunks. Only just, it doesn't make sense to do that because it is several thousand times slower, and at the same time is much more insecure.







    share|improve this answer












    share|improve this answer



    share|improve this answer










    answered 14 hours ago









    DamonDamon

    3,347917




    3,347917













    • vastly inferior? Compare the expand of cryptography after invention on Asymmetric Cryptography.

      – kelalaka
      13 hours ago











    • @kelalaka For communication.

      – wizzwizz4
      4 hours ago



















    • vastly inferior? Compare the expand of cryptography after invention on Asymmetric Cryptography.

      – kelalaka
      13 hours ago











    • @kelalaka For communication.

      – wizzwizz4
      4 hours ago

















    vastly inferior? Compare the expand of cryptography after invention on Asymmetric Cryptography.

    – kelalaka
    13 hours ago





    vastly inferior? Compare the expand of cryptography after invention on Asymmetric Cryptography.

    – kelalaka
    13 hours ago













    @kelalaka For communication.

    – wizzwizz4
    4 hours ago





    @kelalaka For communication.

    – wizzwizz4
    4 hours ago













    10














    Asymmetric encryption like RSA is limited in that you can only use it to encrypt data the size of the key. With a 2048 bit key, you can only encrypt 2048 bits of information. For this reason RSA is unsuitable for bulk encryption like disks - and even for small files like email messages.



    This is why almost all uses of asymmetric encryption involve "hybrid encryption". RSA is used to encrypt the key for a symmetric algorithm like AES, and AES is used to encrypt the bulk data. PGP is an example of a hybrid encryption application.





    Correction - as @HenningMakholm points out in the comments, it isn't that asymmetric can't be chained to handle larger blocks of data the way symmetric algorithms do, it's that doing so is impractical from a performance point of view. The end effect is the same, but the mechanism is different.






    share|improve this answer





















    • 8





      And AES can only encrypt 128 bits of information. There are well-known solutions to using AES for larger amounts of data, and some of them could be applied with RSA as the underlying primitive instead of AES. Performance would be dismal, though, which is the real reason why this is not done.

      – Henning Makholm
      15 hours ago






    • 2





      I'm not sure why this answer has so many upvotes, it's flat-out wrong. That's not the difference between RSA and AES, it's the difference between block-ciphers (including both RSA and AES) and stream ciphers. And it's not even a big deal, since you can easily turn any block cipher into a stream cipher using the various modes.

      – BlueRaja - Danny Pflughoeft
      4 hours ago


















    10














    Asymmetric encryption like RSA is limited in that you can only use it to encrypt data the size of the key. With a 2048 bit key, you can only encrypt 2048 bits of information. For this reason RSA is unsuitable for bulk encryption like disks - and even for small files like email messages.



    This is why almost all uses of asymmetric encryption involve "hybrid encryption". RSA is used to encrypt the key for a symmetric algorithm like AES, and AES is used to encrypt the bulk data. PGP is an example of a hybrid encryption application.





    Correction - as @HenningMakholm points out in the comments, it isn't that asymmetric can't be chained to handle larger blocks of data the way symmetric algorithms do, it's that doing so is impractical from a performance point of view. The end effect is the same, but the mechanism is different.






    share|improve this answer





















    • 8





      And AES can only encrypt 128 bits of information. There are well-known solutions to using AES for larger amounts of data, and some of them could be applied with RSA as the underlying primitive instead of AES. Performance would be dismal, though, which is the real reason why this is not done.

      – Henning Makholm
      15 hours ago






    • 2





      I'm not sure why this answer has so many upvotes, it's flat-out wrong. That's not the difference between RSA and AES, it's the difference between block-ciphers (including both RSA and AES) and stream ciphers. And it's not even a big deal, since you can easily turn any block cipher into a stream cipher using the various modes.

      – BlueRaja - Danny Pflughoeft
      4 hours ago
















    10












    10








    10







    Asymmetric encryption like RSA is limited in that you can only use it to encrypt data the size of the key. With a 2048 bit key, you can only encrypt 2048 bits of information. For this reason RSA is unsuitable for bulk encryption like disks - and even for small files like email messages.



    This is why almost all uses of asymmetric encryption involve "hybrid encryption". RSA is used to encrypt the key for a symmetric algorithm like AES, and AES is used to encrypt the bulk data. PGP is an example of a hybrid encryption application.





    Correction - as @HenningMakholm points out in the comments, it isn't that asymmetric can't be chained to handle larger blocks of data the way symmetric algorithms do, it's that doing so is impractical from a performance point of view. The end effect is the same, but the mechanism is different.






    share|improve this answer















    Asymmetric encryption like RSA is limited in that you can only use it to encrypt data the size of the key. With a 2048 bit key, you can only encrypt 2048 bits of information. For this reason RSA is unsuitable for bulk encryption like disks - and even for small files like email messages.



    This is why almost all uses of asymmetric encryption involve "hybrid encryption". RSA is used to encrypt the key for a symmetric algorithm like AES, and AES is used to encrypt the bulk data. PGP is an example of a hybrid encryption application.





    Correction - as @HenningMakholm points out in the comments, it isn't that asymmetric can't be chained to handle larger blocks of data the way symmetric algorithms do, it's that doing so is impractical from a performance point of view. The end effect is the same, but the mechanism is different.







    share|improve this answer














    share|improve this answer



    share|improve this answer








    edited 12 hours ago

























    answered 21 hours ago









    gowenfawrgowenfawr

    55k11115163




    55k11115163








    • 8





      And AES can only encrypt 128 bits of information. There are well-known solutions to using AES for larger amounts of data, and some of them could be applied with RSA as the underlying primitive instead of AES. Performance would be dismal, though, which is the real reason why this is not done.

      – Henning Makholm
      15 hours ago






    • 2





      I'm not sure why this answer has so many upvotes, it's flat-out wrong. That's not the difference between RSA and AES, it's the difference between block-ciphers (including both RSA and AES) and stream ciphers. And it's not even a big deal, since you can easily turn any block cipher into a stream cipher using the various modes.

      – BlueRaja - Danny Pflughoeft
      4 hours ago
















    • 8





      And AES can only encrypt 128 bits of information. There are well-known solutions to using AES for larger amounts of data, and some of them could be applied with RSA as the underlying primitive instead of AES. Performance would be dismal, though, which is the real reason why this is not done.

      – Henning Makholm
      15 hours ago






    • 2





      I'm not sure why this answer has so many upvotes, it's flat-out wrong. That's not the difference between RSA and AES, it's the difference between block-ciphers (including both RSA and AES) and stream ciphers. And it's not even a big deal, since you can easily turn any block cipher into a stream cipher using the various modes.

      – BlueRaja - Danny Pflughoeft
      4 hours ago










    8




    8





    And AES can only encrypt 128 bits of information. There are well-known solutions to using AES for larger amounts of data, and some of them could be applied with RSA as the underlying primitive instead of AES. Performance would be dismal, though, which is the real reason why this is not done.

    – Henning Makholm
    15 hours ago





    And AES can only encrypt 128 bits of information. There are well-known solutions to using AES for larger amounts of data, and some of them could be applied with RSA as the underlying primitive instead of AES. Performance would be dismal, though, which is the real reason why this is not done.

    – Henning Makholm
    15 hours ago




    2




    2





    I'm not sure why this answer has so many upvotes, it's flat-out wrong. That's not the difference between RSA and AES, it's the difference between block-ciphers (including both RSA and AES) and stream ciphers. And it's not even a big deal, since you can easily turn any block cipher into a stream cipher using the various modes.

    – BlueRaja - Danny Pflughoeft
    4 hours ago







    I'm not sure why this answer has so many upvotes, it's flat-out wrong. That's not the difference between RSA and AES, it's the difference between block-ciphers (including both RSA and AES) and stream ciphers. And it's not even a big deal, since you can easily turn any block cipher into a stream cipher using the various modes.

    – BlueRaja - Danny Pflughoeft
    4 hours ago













    3














    The coldboot attack can be performed on any encryption scheme as long as the keys are residing on the memory. For full-disk encryption (FDE) with symmetric algorithms like AES , you will need to take out the key from the TPM, where you will be applicable to coldboot attack.



    Though the TPM is capable of RSA encryption and decryptions, for FDE the RSA has problems, in short the speed;




    1. RSA must use AOEP scheme to be secure which reduces the message size.

    2. To speed up the public key encryption the public key is selected as 3, 5, ... However, the decryption to access one block will be much more slower even you use CRT to gain 4x speed.

    3. Even the TPM can perform RSA encryption on the chip, it will be much slower for Full Disk Encryption (FDE).


    Therefore, TPM based FDEs use TPM as a key storage.






    share|improve this answer




























      3














      The coldboot attack can be performed on any encryption scheme as long as the keys are residing on the memory. For full-disk encryption (FDE) with symmetric algorithms like AES , you will need to take out the key from the TPM, where you will be applicable to coldboot attack.



      Though the TPM is capable of RSA encryption and decryptions, for FDE the RSA has problems, in short the speed;




      1. RSA must use AOEP scheme to be secure which reduces the message size.

      2. To speed up the public key encryption the public key is selected as 3, 5, ... However, the decryption to access one block will be much more slower even you use CRT to gain 4x speed.

      3. Even the TPM can perform RSA encryption on the chip, it will be much slower for Full Disk Encryption (FDE).


      Therefore, TPM based FDEs use TPM as a key storage.






      share|improve this answer


























        3












        3








        3







        The coldboot attack can be performed on any encryption scheme as long as the keys are residing on the memory. For full-disk encryption (FDE) with symmetric algorithms like AES , you will need to take out the key from the TPM, where you will be applicable to coldboot attack.



        Though the TPM is capable of RSA encryption and decryptions, for FDE the RSA has problems, in short the speed;




        1. RSA must use AOEP scheme to be secure which reduces the message size.

        2. To speed up the public key encryption the public key is selected as 3, 5, ... However, the decryption to access one block will be much more slower even you use CRT to gain 4x speed.

        3. Even the TPM can perform RSA encryption on the chip, it will be much slower for Full Disk Encryption (FDE).


        Therefore, TPM based FDEs use TPM as a key storage.






        share|improve this answer













        The coldboot attack can be performed on any encryption scheme as long as the keys are residing on the memory. For full-disk encryption (FDE) with symmetric algorithms like AES , you will need to take out the key from the TPM, where you will be applicable to coldboot attack.



        Though the TPM is capable of RSA encryption and decryptions, for FDE the RSA has problems, in short the speed;




        1. RSA must use AOEP scheme to be secure which reduces the message size.

        2. To speed up the public key encryption the public key is selected as 3, 5, ... However, the decryption to access one block will be much more slower even you use CRT to gain 4x speed.

        3. Even the TPM can perform RSA encryption on the chip, it will be much slower for Full Disk Encryption (FDE).


        Therefore, TPM based FDEs use TPM as a key storage.







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 12 hours ago









        kelalakakelalaka

        1,2252817




        1,2252817






















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