Note that CRCs are designed to cover a certain message length, and are designed to catch bit errors within that message. The probability of a single bit error g

Note that CRCs are designed to cover a certain message length, and are designed to catch bit errors within that message. The probability of a single bit error getting through is much much greater than a simple probability of 1 in 4 billion, the probability of catching 2 bit errors is somewhat less than catching 1 bit error (but still greater than 1 in 4 billion), and so on. (e.g. https://users.ece.cmu.edu/~koopman/networks/dsn02/dsn02_koopman.pdf https://users.ece.cmu.edu/~koopman/networks/dsn02/dsn02_koop... argues CRC32 will detect all 1, 2 and 3 bit errors in an ethernet frame)