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What are the technical specifications of a private key?
https://getmonero.org/technical-specs/ doesn't say.
https://en.bitcoin.it/wiki/Private_key shows: "In Bitcoin, a private key is a 256-bit number, which can be represented one of several ways. Here is a private key in hexadecimal - 256 bits in hexadecimal is 32 bytes, or 64 characters in the range 0-9 or A-F. "
I need to generate a private key by coin flipping.
A private spend key is a positive integer lesser than l = 7237005577332262213973186563042994240857116359379907606001950938285454250989 (which is a 253-bit integer). The usual process to make a private spend key is to generate a random 256-bit integer and then reduce it modulo l.
The private spend keys are usually represented in one of the following ways:
You can generate the 256-bit number with coin flips, but then you have to compute its remainder modulo l. Also, instead of using a simple coin flip to determine each bit (e.g. 0 for head, 1 for tail), it is better to use double flips to have better randomness in case the coin has a bias (e.g. 0 for head-tail, 1 for tail-head, ignore head-head and tail-tail).
