| 1 | using System; |
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| 2 | using System.Collections.Generic; |
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| 3 | using System.Text; |
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| 4 | |
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| 5 | using Eraser.Manager; |
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| 6 | using System.IO; |
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| 7 | |
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| 8 | namespace Eraser.DefaultPlugins |
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| 9 | { |
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| 10 | class FirstLast16KB : ErasureMethod |
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| 11 | { |
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| 12 | public override string Name |
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| 13 | { |
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| 14 | get { return "First/last 16KB Erasure"; } |
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| 15 | } |
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| 16 | |
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| 17 | public override int Passes |
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| 18 | { |
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| 19 | get { return 0; } //Variable number, depending on defaults. |
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| 20 | } |
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| 21 | |
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| 22 | public override Guid GUID |
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| 23 | { |
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| 24 | get { return new Guid("{0C2E07BF-0207-49a3-ADE8-46F9E1499C01}"); } |
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| 25 | } |
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| 26 | |
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| 27 | public override long CalculateEraseDataSize(List<string> paths, long targetSize) |
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| 28 | { |
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| 29 | //Amount of data required to be written. |
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| 30 | long amountToWrite = 0; |
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| 31 | if (paths == null) |
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| 32 | { |
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| 33 | if (targetSize <= dataSize) |
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| 34 | amountToWrite = targetSize; |
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| 35 | else |
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| 36 | amountToWrite = dataSize * 2; |
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| 37 | } |
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| 38 | else |
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| 39 | amountToWrite = paths.Count * dataSize * 2; |
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| 40 | |
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| 41 | //The final amount has to be multiplied by the number of passes. |
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| 42 | return amountToWrite * Method.Passes; |
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| 43 | } |
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| 44 | |
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| 45 | public override void Erase(Stream strm, long erasureLength, PRNG prng, |
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| 46 | OnProgress callback) |
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| 47 | { |
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| 48 | //Make sure that the erasureLength passed in here is the maximum value |
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| 49 | //for the size of long, since we don't want to write extra or write |
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| 50 | //less. |
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| 51 | if (erasureLength != long.MaxValue) |
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| 52 | throw new ArgumentException("The amount of data erased should not be " + |
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| 53 | "limited, since this is a self-limiting erasure method."); |
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| 54 | |
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| 55 | ErasureMethod method = Method; |
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| 56 | |
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| 57 | //If the target stream is shorter than 16kb, just forward it to the default |
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| 58 | //function. |
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| 59 | if (strm.Length < dataSize) |
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| 60 | { |
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| 61 | method.Erase(strm, erasureLength, prng, callback); |
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| 62 | return; |
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| 63 | } |
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| 64 | |
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| 65 | //Seek to the beginning and write 16kb. |
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| 66 | strm.Seek(0, SeekOrigin.Begin); |
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| 67 | method.Erase(strm, dataSize, prng, callback); |
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| 68 | |
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| 69 | //Seek to the end - 16kb, and write. |
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| 70 | strm.Seek(-dataSize, SeekOrigin.End); |
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| 71 | method.Erase(strm, long.MaxValue, prng, callback); |
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| 72 | } |
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| 73 | |
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| 74 | private ErasureMethod Method |
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| 75 | { |
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| 76 | get |
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| 77 | { |
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| 78 | //Try to retrieve the default erasure method. |
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| 79 | ErasureMethod defaultMethod = ErasureMethodManager.GetInstance( |
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| 80 | Globals.Settings.DefaultFileErasureMethod); |
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| 81 | |
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| 82 | //If we are the default, use the default pseudorandom pass. |
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| 83 | if (defaultMethod.GUID == GUID) |
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| 84 | defaultMethod = ErasureMethodManager.GetInstance(new Guid( |
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| 85 | "{BF8BA267-231A-4085-9BF9-204DE65A6641}")); |
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| 86 | |
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| 87 | return defaultMethod; |
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| 88 | } |
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| 89 | } |
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| 90 | |
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| 91 | /// <summary> |
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| 92 | /// The amount of data to be erased from the header and the end of the file. |
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| 93 | /// </summary> |
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| 94 | private const long dataSize = 16 * 1024; |
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| 95 | } |
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| 96 | } |
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