CRYPTO_MEMCMP(3)

💖 NAME 💖

okay so welcome to the CRYPTO_memcmp(3) page from the Library Functions Manual, aka the libcrypto girlie 💅 this one is all about constant time memory comparison — no cap, it's giving secure little helper energy 🫶

✨ SYNOPSIS ✨

library “libcrypto” #include <openssl/crypto.h>

int
CRYPTO_memcmp(const void *a, const void *b, size_t len);

🌸 DESCRIPTION 🌸

CRYPTO_memcmp() compares the len bytes pointed to by a and b for equality 💖

the way it works timing-wise: it takes an amount of time dependent on len, but independent of the contents of the memory regions pointed to by a and b ✨ so the clock is basically like “how many bytes, bestie?” and not “what’s inside them?” 🎀

🦋 RETURN VALUES 🦋

• CRYPTO_memcmp() returns 0 if the content of the memory regions is equal 💚
• or non-zero otherwise 💀

🌈 HISTORY 🌈

• CRYPTO_memcmp() first appeared in OpenSSL 1.0.1d 🔥
• and has been available since OpenBSD 5.6 👑

💀 BUGS 💀

• unlike memcmp(3) and timingsafe_memcmp(3), this function cannot be used to order the two memory regions 🙈 like, it is not a sorting vibe, periodt
• in the current implementation, the return value is always greater than or equal to 0 🧚

xoxo, this page is from Debian and dated June 8, 2025 🎀 stay constant-time, bestie 💜