Ruby SHA2 digest incorrect doc or issue in my IRB?

Question

The doc @ http://www.ruby-doc.org/stdlib-1.9.3/libdoc/digest/rdoc/Digest/SHA2.html shows:

Digest::SHA256.new.digest_length * 8
 #=> 512
Digest::SHA384.new.digest_length * 8
 #=> 1024
Digest::SHA512.new.digest_length * 8
 #=> 1024

Here's my output in 2.1.3:

Digest::SHA256.new.digest_length * 8
 #=> 256 
Digest::SHA384.new.digest_length * 8
 #=> 384 
Digest::SHA512.new.digest_length * 8
 #=> 512

Why does my block length output differ from Ruby docs?

Answer 1

Seems like there is a typo in docs, look,

block_length → Integer
Returns the block length of the digest in bytes.

Digest::SHA256.new.digest_length * 8
# => 512
Digest::SHA384.new.digest_length * 8
# => 1024
Digest::SHA512.new.digest_length * 8
# => 1024

digest_length → Integer
Returns the length of the hash value of the digest in bytes.

Digest::SHA256.new.digest_length * 8
# => 256
Digest::SHA384.new.digest_length * 8
# => 384
Digest::SHA512.new.digest_length * 8
# => 512

Both are using digest_length in examples.

But instead it should be,

block_length → Integer
Returns the block length of the digest in bytes.

Digest::SHA256.new.block_length * 8
# => 512
Digest::SHA384.new.block_length * 8
# => 1024
Digest::SHA512.new.block_length * 8
# => 1024

digest_length → Integer
Returns the length of the hash value of the digest in bytes.

Digest::SHA256.new.digest_length * 8
# => 256
Digest::SHA384.new.digest_length * 8
# => 384
Digest::SHA512.new.digest_length * 8
# => 512

Answer 2

This has been fixed in the 2.0.0 documentation (commit)

There appears to be mistake in the Ruby 1.9.3 documentation for the method Digest::SHA2#block_length, as they are using the digest_length method instead of block_length in the examples.

Using digest_block actually gets the shown values 512, 1024, and 1024:

Digest::SHA256.new.block_length * 8
# => 512

Digest::SHA384.new.block_length * 8
# => 1024

Digest::SHA512.new.block_length * 8
# => 1024