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doc: Add chunker_polynomial

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Alexander Neumann 2015-04-07 20:09:25 +02:00
parent 9a5864642a
commit 8fb032b590
1 changed files with 9 additions and 6 deletions
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doc/Design.md
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@ -1,4 +1,5 @@
This document gives a high-level overview of the design and repository layout of the restic backup program. This document gives a high-level overview of the design and repository layout
of the restic backup program.
Repository Format Repository Format
================= =================
@ -121,9 +122,9 @@ last 32 byte). If the password is incorrect or the key file has been tampered
with, the computed MAC will not match the last 16 bytes of the data, and with, the computed MAC will not match the last 16 bytes of the data, and
restic exits with an error. Otherwise, the data is decrypted with the restic exits with an error. Otherwise, the data is decrypted with the
encryption key derived from `scrypt`. This yields a JSON document which encryption key derived from `scrypt`. This yields a JSON document which
contains the master signing and encryption keys for this repository, encoded in contains the master signing and encryption keys for this repository (encoded in
Base64. The command `restic cat masterkey` can be used as follows to decrypt Base64) and the polynomial that is used for CDC. The command `restic cat
and pretty-print the master key: masterkey` can be used as follows to decrypt and pretty-print the master key:
$ restic -r /tmp/restic-repo cat masterkey $ restic -r /tmp/restic-repo cat masterkey
{ {
@ -131,7 +132,8 @@ and pretty-print the master key:
"k": "evFWd9wWlndL9jc501268g==", "k": "evFWd9wWlndL9jc501268g==",
"r": "E9eEDnSJZgqwTOkDtOp+Dw==" "r": "E9eEDnSJZgqwTOkDtOp+Dw=="
}, },
"encrypt": "UQCqa0lKZ94PygPxMRqkePTZnHRYh1k1pX2k2lM2v3Q=" "encrypt": "UQCqa0lKZ94PygPxMRqkePTZnHRYh1k1pX2k2lM2v3Q=",
"chunker_polynomial": "2f0797d9c2363f"
} }
All data in the repository is encrypted and signed with these master keys with All data in the repository is encrypted and signed with these master keys with
@ -292,7 +294,8 @@ For creating a backup, restic scans the target directory for all files,
sub-directories and other entries. The data from each file is split into sub-directories and other entries. The data from each file is split into
variable length chunks cut at offsets defined by a sliding window of 64 byte. variable length chunks cut at offsets defined by a sliding window of 64 byte.
The implementation uses Rabin Fingerprints for implementing this Content The implementation uses Rabin Fingerprints for implementing this Content
Defined Chunking (CDC). Defined Chunking (CDC). An irreducible polynomial is selected at random when a
repository is initialized.
Files smaller than 512 KiB are not split, chunks are of 512 KiB to 8 MiB in Files smaller than 512 KiB are not split, chunks are of 512 KiB to 8 MiB in
size. The implementation aims for 1 MiB chunk size on average. size. The implementation aims for 1 MiB chunk size on average.