Does the hash of a file change if the filename changes?












4















Does the hash of a file change if the filename or path or timestamp or permissions change?



$ echo some contents > testfile

$ shasum testfile 

3a2be7b07a1a19072bf54c95a8c4a3fe0cdb35d4  testfile





hashsum







share|improve this question


















  • 1





    If you need it to, then you can zip it.

    – ctrl-alt-delor
    Aug 3 '15 at 22:48
















4















Does the hash of a file change if the filename or path or timestamp or permissions change?



$ echo some contents > testfile

$ shasum testfile 

3a2be7b07a1a19072bf54c95a8c4a3fe0cdb35d4  testfile





hashsum







share|improve this question


















  • 1





    If you need it to, then you can zip it.

    – ctrl-alt-delor
    Aug 3 '15 at 22:48














4












4








4


1






Does the hash of a file change if the filename or path or timestamp or permissions change?



$ echo some contents > testfile

$ shasum testfile 

3a2be7b07a1a19072bf54c95a8c4a3fe0cdb35d4  testfile





hashsum







share|improve this question














Does the hash of a file change if the filename or path or timestamp or permissions change?



$ echo some contents > testfile

$ shasum testfile 

3a2be7b07a1a19072bf54c95a8c4a3fe0cdb35d4  testfile





hashsum




hashsum






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Aug 3 '15 at 22:41









tarabytetarabyte

1,00251832




1,00251832








  • 1





    If you need it to, then you can zip it.

    – ctrl-alt-delor
    Aug 3 '15 at 22:48














  • 1





    If you need it to, then you can zip it.

    – ctrl-alt-delor
    Aug 3 '15 at 22:48








1




1





If you need it to, then you can zip it.

– ctrl-alt-delor
Aug 3 '15 at 22:48





If you need it to, then you can zip it.

– ctrl-alt-delor
Aug 3 '15 at 22:48










2 Answers
2






active

oldest

votes


















7














The hash of a file is the hash of its contents. Metadata such as the file name, timestamps, permissions, etc. have no influence on the hash.



Assuming a non-broken cryptographic hash, two files have the same hash if and only if they have the same contents. The most common such hashes are the SHA-2 family (SHA-256, SHA-384, SHA-512) and the SHA3 family. This does not include MD5 or SHA-1 which are broken, nor a CRC such as with cksum which is not a cryptographic hash.






share|improve this answer





















  • 1





    In general, all hashes have collisions. A non-broken cryptographic hash implies that there is no efficient way to generate a collision.

    – Tyson Williams
    Jan 23 at 15:29











  • @TysonWilliams That's true but irrelevant. If you have two files with the same hash, and the hash is a non-broken cryptographic hash, then the two files have the same hash if and only if they have the same contents. If you could find a collision, it wouldn't be a non-broken cryptographic hash.

    – Gilles
    Jan 23 at 22:23






  • 1





    What you said is false. Every (practical) hash function, even non-broken cryptographic ones, have collisions. There are more inputs than outputs, so by the pigeonhole principle, there must be a collision.

    – Tyson Williams
    Jan 23 at 22:29













  • @TysonWilliams But I never claimed that there were no collisions. Of course there are collisions. But 1. it's extremely rare to find collisions for what is generally considered to be a non-broken cryptographic hash function, and 2. if someone did find a collision then that function would no longer be a non-broken cryptographic hash function. In practical terms, if you have two files with the same SHA-256 hash, they have identical contents.

    – Gilles
    Jan 23 at 22:33






  • 1





    The statement "f you have two files with the same hash, and the hash is a non-broken cryptographic hash, then the two files have the same hash if and only if they have the same contents." is equivalent to "non-broken cryptographic hash [functions] have no collisions". I agree that "In practical terms, if you have two files with the same SHA-256 hash, they have identical contents."

    – Tyson Williams
    Jan 23 at 22:36



















4














Not as far as I can tell after a simple test.



$ echo some contents > testfile

$ shasum testfile 

3a2be7b07a1a19072bf54c95a8c4a3fe0cdb35d4  testfile

$ mv testfile newfile

$ shasum newfile 

3a2be7b07a1a19072bf54c95a8c4a3fe0cdb35d4  newfile





share|improve this answer



















  • 1





    But note that if you blindly compare the outputs of shasum, they will not match since the output includes the filename/path (as shown in your example). A good workaround is to do something like shasum - < testfile.

    – DoxyLover
    Aug 3 '15 at 22:53











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2 Answers
2






active

oldest

votes








2 Answers
2






active

oldest

votes









active

oldest

votes






active

oldest

votes









7














The hash of a file is the hash of its contents. Metadata such as the file name, timestamps, permissions, etc. have no influence on the hash.



Assuming a non-broken cryptographic hash, two files have the same hash if and only if they have the same contents. The most common such hashes are the SHA-2 family (SHA-256, SHA-384, SHA-512) and the SHA3 family. This does not include MD5 or SHA-1 which are broken, nor a CRC such as with cksum which is not a cryptographic hash.






share|improve this answer





















  • 1





    In general, all hashes have collisions. A non-broken cryptographic hash implies that there is no efficient way to generate a collision.

    – Tyson Williams
    Jan 23 at 15:29











  • @TysonWilliams That's true but irrelevant. If you have two files with the same hash, and the hash is a non-broken cryptographic hash, then the two files have the same hash if and only if they have the same contents. If you could find a collision, it wouldn't be a non-broken cryptographic hash.

    – Gilles
    Jan 23 at 22:23






  • 1





    What you said is false. Every (practical) hash function, even non-broken cryptographic ones, have collisions. There are more inputs than outputs, so by the pigeonhole principle, there must be a collision.

    – Tyson Williams
    Jan 23 at 22:29













  • @TysonWilliams But I never claimed that there were no collisions. Of course there are collisions. But 1. it's extremely rare to find collisions for what is generally considered to be a non-broken cryptographic hash function, and 2. if someone did find a collision then that function would no longer be a non-broken cryptographic hash function. In practical terms, if you have two files with the same SHA-256 hash, they have identical contents.

    – Gilles
    Jan 23 at 22:33






  • 1





    The statement "f you have two files with the same hash, and the hash is a non-broken cryptographic hash, then the two files have the same hash if and only if they have the same contents." is equivalent to "non-broken cryptographic hash [functions] have no collisions". I agree that "In practical terms, if you have two files with the same SHA-256 hash, they have identical contents."

    – Tyson Williams
    Jan 23 at 22:36
















7














The hash of a file is the hash of its contents. Metadata such as the file name, timestamps, permissions, etc. have no influence on the hash.



Assuming a non-broken cryptographic hash, two files have the same hash if and only if they have the same contents. The most common such hashes are the SHA-2 family (SHA-256, SHA-384, SHA-512) and the SHA3 family. This does not include MD5 or SHA-1 which are broken, nor a CRC such as with cksum which is not a cryptographic hash.






share|improve this answer





















  • 1





    In general, all hashes have collisions. A non-broken cryptographic hash implies that there is no efficient way to generate a collision.

    – Tyson Williams
    Jan 23 at 15:29











  • @TysonWilliams That's true but irrelevant. If you have two files with the same hash, and the hash is a non-broken cryptographic hash, then the two files have the same hash if and only if they have the same contents. If you could find a collision, it wouldn't be a non-broken cryptographic hash.

    – Gilles
    Jan 23 at 22:23






  • 1





    What you said is false. Every (practical) hash function, even non-broken cryptographic ones, have collisions. There are more inputs than outputs, so by the pigeonhole principle, there must be a collision.

    – Tyson Williams
    Jan 23 at 22:29













  • @TysonWilliams But I never claimed that there were no collisions. Of course there are collisions. But 1. it's extremely rare to find collisions for what is generally considered to be a non-broken cryptographic hash function, and 2. if someone did find a collision then that function would no longer be a non-broken cryptographic hash function. In practical terms, if you have two files with the same SHA-256 hash, they have identical contents.

    – Gilles
    Jan 23 at 22:33






  • 1





    The statement "f you have two files with the same hash, and the hash is a non-broken cryptographic hash, then the two files have the same hash if and only if they have the same contents." is equivalent to "non-broken cryptographic hash [functions] have no collisions". I agree that "In practical terms, if you have two files with the same SHA-256 hash, they have identical contents."

    – Tyson Williams
    Jan 23 at 22:36














7












7








7







The hash of a file is the hash of its contents. Metadata such as the file name, timestamps, permissions, etc. have no influence on the hash.



Assuming a non-broken cryptographic hash, two files have the same hash if and only if they have the same contents. The most common such hashes are the SHA-2 family (SHA-256, SHA-384, SHA-512) and the SHA3 family. This does not include MD5 or SHA-1 which are broken, nor a CRC such as with cksum which is not a cryptographic hash.






share|improve this answer















The hash of a file is the hash of its contents. Metadata such as the file name, timestamps, permissions, etc. have no influence on the hash.



Assuming a non-broken cryptographic hash, two files have the same hash if and only if they have the same contents. The most common such hashes are the SHA-2 family (SHA-256, SHA-384, SHA-512) and the SHA3 family. This does not include MD5 or SHA-1 which are broken, nor a CRC such as with cksum which is not a cryptographic hash.







share|improve this answer














share|improve this answer



share|improve this answer








edited Jan 23 at 22:25

























answered Aug 4 '15 at 1:09









GillesGilles

534k12810791597




534k12810791597








  • 1





    In general, all hashes have collisions. A non-broken cryptographic hash implies that there is no efficient way to generate a collision.

    – Tyson Williams
    Jan 23 at 15:29











  • @TysonWilliams That's true but irrelevant. If you have two files with the same hash, and the hash is a non-broken cryptographic hash, then the two files have the same hash if and only if they have the same contents. If you could find a collision, it wouldn't be a non-broken cryptographic hash.

    – Gilles
    Jan 23 at 22:23






  • 1





    What you said is false. Every (practical) hash function, even non-broken cryptographic ones, have collisions. There are more inputs than outputs, so by the pigeonhole principle, there must be a collision.

    – Tyson Williams
    Jan 23 at 22:29













  • @TysonWilliams But I never claimed that there were no collisions. Of course there are collisions. But 1. it's extremely rare to find collisions for what is generally considered to be a non-broken cryptographic hash function, and 2. if someone did find a collision then that function would no longer be a non-broken cryptographic hash function. In practical terms, if you have two files with the same SHA-256 hash, they have identical contents.

    – Gilles
    Jan 23 at 22:33






  • 1





    The statement "f you have two files with the same hash, and the hash is a non-broken cryptographic hash, then the two files have the same hash if and only if they have the same contents." is equivalent to "non-broken cryptographic hash [functions] have no collisions". I agree that "In practical terms, if you have two files with the same SHA-256 hash, they have identical contents."

    – Tyson Williams
    Jan 23 at 22:36














  • 1





    In general, all hashes have collisions. A non-broken cryptographic hash implies that there is no efficient way to generate a collision.

    – Tyson Williams
    Jan 23 at 15:29











  • @TysonWilliams That's true but irrelevant. If you have two files with the same hash, and the hash is a non-broken cryptographic hash, then the two files have the same hash if and only if they have the same contents. If you could find a collision, it wouldn't be a non-broken cryptographic hash.

    – Gilles
    Jan 23 at 22:23






  • 1





    What you said is false. Every (practical) hash function, even non-broken cryptographic ones, have collisions. There are more inputs than outputs, so by the pigeonhole principle, there must be a collision.

    – Tyson Williams
    Jan 23 at 22:29













  • @TysonWilliams But I never claimed that there were no collisions. Of course there are collisions. But 1. it's extremely rare to find collisions for what is generally considered to be a non-broken cryptographic hash function, and 2. if someone did find a collision then that function would no longer be a non-broken cryptographic hash function. In practical terms, if you have two files with the same SHA-256 hash, they have identical contents.

    – Gilles
    Jan 23 at 22:33






  • 1





    The statement "f you have two files with the same hash, and the hash is a non-broken cryptographic hash, then the two files have the same hash if and only if they have the same contents." is equivalent to "non-broken cryptographic hash [functions] have no collisions". I agree that "In practical terms, if you have two files with the same SHA-256 hash, they have identical contents."

    – Tyson Williams
    Jan 23 at 22:36








1




1





In general, all hashes have collisions. A non-broken cryptographic hash implies that there is no efficient way to generate a collision.

– Tyson Williams
Jan 23 at 15:29





In general, all hashes have collisions. A non-broken cryptographic hash implies that there is no efficient way to generate a collision.

– Tyson Williams
Jan 23 at 15:29













@TysonWilliams That's true but irrelevant. If you have two files with the same hash, and the hash is a non-broken cryptographic hash, then the two files have the same hash if and only if they have the same contents. If you could find a collision, it wouldn't be a non-broken cryptographic hash.

– Gilles
Jan 23 at 22:23





@TysonWilliams That's true but irrelevant. If you have two files with the same hash, and the hash is a non-broken cryptographic hash, then the two files have the same hash if and only if they have the same contents. If you could find a collision, it wouldn't be a non-broken cryptographic hash.

– Gilles
Jan 23 at 22:23




1




1





What you said is false. Every (practical) hash function, even non-broken cryptographic ones, have collisions. There are more inputs than outputs, so by the pigeonhole principle, there must be a collision.

– Tyson Williams
Jan 23 at 22:29







What you said is false. Every (practical) hash function, even non-broken cryptographic ones, have collisions. There are more inputs than outputs, so by the pigeonhole principle, there must be a collision.

– Tyson Williams
Jan 23 at 22:29















@TysonWilliams But I never claimed that there were no collisions. Of course there are collisions. But 1. it's extremely rare to find collisions for what is generally considered to be a non-broken cryptographic hash function, and 2. if someone did find a collision then that function would no longer be a non-broken cryptographic hash function. In practical terms, if you have two files with the same SHA-256 hash, they have identical contents.

– Gilles
Jan 23 at 22:33





@TysonWilliams But I never claimed that there were no collisions. Of course there are collisions. But 1. it's extremely rare to find collisions for what is generally considered to be a non-broken cryptographic hash function, and 2. if someone did find a collision then that function would no longer be a non-broken cryptographic hash function. In practical terms, if you have two files with the same SHA-256 hash, they have identical contents.

– Gilles
Jan 23 at 22:33




1




1





The statement "f you have two files with the same hash, and the hash is a non-broken cryptographic hash, then the two files have the same hash if and only if they have the same contents." is equivalent to "non-broken cryptographic hash [functions] have no collisions". I agree that "In practical terms, if you have two files with the same SHA-256 hash, they have identical contents."

– Tyson Williams
Jan 23 at 22:36





The statement "f you have two files with the same hash, and the hash is a non-broken cryptographic hash, then the two files have the same hash if and only if they have the same contents." is equivalent to "non-broken cryptographic hash [functions] have no collisions". I agree that "In practical terms, if you have two files with the same SHA-256 hash, they have identical contents."

– Tyson Williams
Jan 23 at 22:36













4














Not as far as I can tell after a simple test.



$ echo some contents > testfile

$ shasum testfile 

3a2be7b07a1a19072bf54c95a8c4a3fe0cdb35d4  testfile

$ mv testfile newfile

$ shasum newfile 

3a2be7b07a1a19072bf54c95a8c4a3fe0cdb35d4  newfile





share|improve this answer



















  • 1





    But note that if you blindly compare the outputs of shasum, they will not match since the output includes the filename/path (as shown in your example). A good workaround is to do something like shasum - < testfile.

    – DoxyLover
    Aug 3 '15 at 22:53
















4














Not as far as I can tell after a simple test.



$ echo some contents > testfile

$ shasum testfile 

3a2be7b07a1a19072bf54c95a8c4a3fe0cdb35d4  testfile

$ mv testfile newfile

$ shasum newfile 

3a2be7b07a1a19072bf54c95a8c4a3fe0cdb35d4  newfile





share|improve this answer



















  • 1





    But note that if you blindly compare the outputs of shasum, they will not match since the output includes the filename/path (as shown in your example). A good workaround is to do something like shasum - < testfile.

    – DoxyLover
    Aug 3 '15 at 22:53














4












4








4







Not as far as I can tell after a simple test.



$ echo some contents > testfile

$ shasum testfile 

3a2be7b07a1a19072bf54c95a8c4a3fe0cdb35d4  testfile

$ mv testfile newfile

$ shasum newfile 

3a2be7b07a1a19072bf54c95a8c4a3fe0cdb35d4  newfile





share|improve this answer













Not as far as I can tell after a simple test.



$ echo some contents > testfile

$ shasum testfile 

3a2be7b07a1a19072bf54c95a8c4a3fe0cdb35d4  testfile

$ mv testfile newfile

$ shasum newfile 

3a2be7b07a1a19072bf54c95a8c4a3fe0cdb35d4  newfile






share|improve this answer












share|improve this answer



share|improve this answer










answered Aug 3 '15 at 22:42









tarabytetarabyte

1,00251832




1,00251832








  • 1





    But note that if you blindly compare the outputs of shasum, they will not match since the output includes the filename/path (as shown in your example). A good workaround is to do something like shasum - < testfile.

    – DoxyLover
    Aug 3 '15 at 22:53














  • 1





    But note that if you blindly compare the outputs of shasum, they will not match since the output includes the filename/path (as shown in your example). A good workaround is to do something like shasum - < testfile.

    – DoxyLover
    Aug 3 '15 at 22:53








1




1





But note that if you blindly compare the outputs of shasum, they will not match since the output includes the filename/path (as shown in your example). A good workaround is to do something like shasum - < testfile.

– DoxyLover
Aug 3 '15 at 22:53





But note that if you blindly compare the outputs of shasum, they will not match since the output includes the filename/path (as shown in your example). A good workaround is to do something like shasum - < testfile.

– DoxyLover
Aug 3 '15 at 22:53


















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