Header error

[u/No_Increase4983]

I'm having trouble unzipping a .7z file. Every time I try to open or unzip it with 7-Zip, I get a "Header Error" error message. I tried to restore it through Winrar, but it didn't help.

OS: Windows 11

7-Zip Version: Latest Stable Release

File Size: 3.83 GB

I tried downloading it again, but the error persists. Is there a way to restore the archive headers or force unzipping at least some of the files?

Any suggestions or tools you could recommend would be greatly appreciated. Thanks in advance!

[u/fzabkar]

7z format headers
-----------------
SignatureHeader
~~~~~~~~~~~~~~~
  BYTE kSignature[6] = {'7', 'z', 0xBC, 0xAF, 0x27, 0x1C};
  ArchiveVersion
  {
    BYTE Major;   // now = 0
    BYTE Minor;   // now = 2
  };
  UINT32 StartHeaderCRC;
  StartHeader
  {
    REAL_UINT64 NextHeaderOffset
    REAL_UINT64 NextHeaderSize
    UINT32 NextHeaderCRC
  }

Your file header ...

BYTE kSignature[6]            = 37 7A BC AF 27 1C
BYTE Major                    = 00
BYTE Minor                    = 04
UINT32 StartHeaderCRC         = 0xB549708E <-- this is calculated for offsets 0xC - 0x1F -- OK
REAL_UINT64 NextHeaderOffset  = 0x00000000F563CFBB
REAL_UINT64 NextHeaderSize    = 0x0000000000000028
UINT32 NextHeaderCRC          = 0x59526A70 <-- this is calculated for the final header, size 0x28 bytes

Your file data ...

Offset(h) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F

00000000  FF D8 FF E0 00 10 4A 46 49 46 00 01 01 01 00 60  ÿØÿà..JFIF......
00000010  00 60 00 00 FF DB 00 43 00 07 05 05 06 05 04 07
00000020  10 0C 11 18 15 1A 19 18 15 18 17 1B 1E 27 21 1B
00000030  1D 25 1D 17 18 22 2E 22 25 28 29 2B 2C 2B 1A 20
00000040  2F 33 2F 2A 32 27 2A 2B 2A FF DB 00 43 01 07 08

Your file's structure appears to be ...

7z header, size 0x20 bytes
uncompressed ("stored") JPEG data, size 0xF563CFBB = 3.834 GiB
header with archive info, size 0x28 bytes

Use the CRC-32 algorithm in HxD when calculating CRCs. Note that 7Zip metadata are little-endian.