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| 1 | Warning | ||
| 2 | ======= | ||
| 3 | Mat only removes metadata from your files, it does not anonymise their | ||
| 4 | content, nor can it handle watermarking, steganography, or any too custom | ||
| 5 | metadata field/system. | ||
| 6 | |||
| 7 | If you really want to be anonymous format that does not contain any | ||
| 8 | metadata, or better : use plain-text. | ||
| 9 | |||
| 10 | Implementation notes | ||
| 11 | ====================== | ||
| 12 | Symlink attacks | ||
| 13 | --------------- | ||
| 14 | MAT output predictable filenames (like yourfile.jpg.bak). | ||
| 15 | This may lead to symlink attack. Please check if you OS prevent | ||
| 16 | against them | ||
| 17 | |||
| 18 | Test suite | ||
| 19 | ---------- | ||
| 20 | Formats that are not in the test suite are not well-tested, | ||
| 21 | please do not trust the MAT about them! | ||
| 22 | |||
| 23 | Threat Model | ||
| 24 | ============ | ||
| 25 | The Metadata Anonymisation Toolkit adversary has a number | ||
| 26 | of goals, capabilities, and counter-attack types that can be | ||
| 27 | used to guide us towards a set of requirements for the MAT. | ||
| 28 | |||
| 29 | Adversary | ||
| 30 | ------------ | ||
| 31 | |||
| 32 | * Goals: | ||
| 33 | |||
| 34 | - Identifying the source of the document, since a document | ||
| 35 | always has one. Who/where/when/how was a picture | ||
| 36 | taken, where was the document leaked from and by | ||
| 37 | whom, ... | ||
| 38 | |||
| 39 | - Identify the author; in some cases documents may be | ||
| 40 | anonymously authored or created. In these cases, | ||
| 41 | identifying the author is the goal. | ||
| 42 | |||
| 43 | - Identify the equipment/software used. If the attacker fails | ||
| 44 | to directly identify the author and/or source, his next | ||
| 45 | goal is to determine the source of the equipment used | ||
| 46 | to produce, copy, and transmit the document. This can | ||
| 47 | include the model of camera used to take a photo, or | ||
| 48 | which software was used to produce an office document. | ||
| 49 | |||
| 50 | |||
| 51 | * Adversary Capabilities - Positioning | ||
| 52 | - The adversary created the document specifically for this | ||
| 53 | user. This is the strongest position for the adversary to | ||
| 54 | have. In this case, the adversary is capable of inserting | ||
| 55 | arbitrary, custom watermarks specifically for tracking | ||
| 56 | the user. In general, MAT cannot defend against this | ||
| 57 | adversary, but we list it for completeness. | ||
| 58 | |||
| 59 | - The adversary created the document for a group of users. | ||
| 60 | In this case, the adversary knows that they attempted to | ||
| 61 | limit distribution to a specific group of users. They may | ||
| 62 | or may not have watermarked the document for these | ||
| 63 | users, but they certainly know the format used. | ||
| 64 | |||
| 65 | - The adversary did not create the document, the weakest | ||
| 66 | position for the adversary to have. The file format is (most of the time) | ||
| 67 | standard, nothing custom is added: MAT | ||
| 68 | should be able to remove all meta-information from the | ||
| 69 | file. | ||
| 70 | |||
| 71 | Requirements | ||
| 72 | --------------- | ||
| 73 | |||
| 74 | * Processing | ||
| 75 | - The MAT *should* avoid interactions with information. | ||
| 76 | Its goal is to remove metadata, and the user is solely | ||
| 77 | responsible for the information of the file. | ||
| 78 | |||
| 79 | - The MAT *must* warn when encountering an unknown | ||
| 80 | format. For example, in a zipfile, if MAT encounters an | ||
| 81 | unknown format, it should warn the user, and ask if the | ||
| 82 | file should be added to the anonymised archive that is | ||
| 83 | produced. | ||
| 84 | |||
| 85 | - The MAT *must* not add metadata, since its purpose is to | ||
| 86 | anonymise files: every added items of metadata decreases | ||
| 87 | anonymity. | ||
| 88 | |||
| 89 | - The MAT *must* handle unknown/hidden metadata fields, | ||
| 90 | like proprietary extensions of open formats. | ||
