endianness

Description

Solution

1. Step 1Capture the prompt
   The server prints a word (e.g., ffoxf). Convert it to hex - ffoxf → 66 66 6f 78 66.
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   Each character maps to its ASCII hex value. ASCII is a 7-bit encoding where printable characters start at 0x20 (space) and run through 0x7E (~). You can look them up with man ascii or use Python: hex(ord('f')) → 0x66.

   The server is essentially asking: "if you stored this 5-character string in memory as a 32/40-bit integer, what bytes would you actually see?" To answer, you first need to know what bytes the characters correspond to - hence the ASCII conversion step.

2. Step 2Flip to little endian
   Reverse the byte order: 66 78 6f 66 66. Submit without spaces/0x prefix (66786f6666).

   66786f6666

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   Endianness describes the order in which bytes of a multi-byte value are stored in memory.

   • Big endian - most significant byte first. The "natural" order, like reading a number left-to-right. Network protocols (TCP/IP) use big endian, which is why it's also called network byte order.
   • Little endian - least significant byte first. x86 and ARM (in most modes) use this. So the number 0x12345678 is stored in memory as 78 56 34 12.

   This matters enormously in low-level programming: if you write a 32-bit integer to a file on an x86 machine and read it back on a big-endian system (some older MIPS, SPARC, PowerPC), the bytes are in the wrong order and the value comes out completely wrong. File formats like PNG and JPEG hard-code big endian (network order) in their specs so they're portable across architectures. Reverse-engineering binary file formats often requires knowing which endianness the original platform used.

Alternate Solution

Related guides

Flag

picoCTF{3ndi4n_sw4p_su33ess_d58...}

After a handful of conversions the service prints the flag.