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If I use openssl to generate some random data (for a keyfile, for example):

openssl rand -hex 2048 >/tmp/file

Is this 4097 bits (or bytes?) of entropy?

-rw-rw-r-- 1 username username 4097 Oct 30 20:01 /tmp/file
  • It's 2048 bytes, hex-encoded (ie a byte = 69 in decimal will be printed as '45') and followed by a newline (2048 * 2 + 1). If you want to raw bytes, don't use the -hex option ;-) – mosvy Oct 31 '18 at 9:55
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Is this 4097 bits (or bytes?) of entropy?

Neither. Entropy is a property of how the random data was generated (see, e.g., this Crypto.SE post), not how much of it was generated. If openssl rand could generate data with x bits of entropy, that would still be x bits of entropy irrespective of whether you told it to output 1 bit or 1 TB.

A detailed discussion of entropy would likely be off-topic here. Maybe ask on Cryptography SE.

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