add sha-3 exposition

doc/hash2/hashing_bytes.adoc

@@ -289,6 +289,22 @@ as SHA2-256 on a 64 bit platform, but twice as slow in 32 bit code.
 On 64 bit platforms, SHA2-512/256 and SHA2-512/224 should be preferred over SHA2-256 and SHA2-224 not just because of speed, but because
 they are resistant to length extension attacks as they don't expose all of the bits of their internal state in the final digest.
 
+### SHA-3
+
+https://en.wikipedia.org/wiki/SHA-3[SHA-3] is the most recent addition to the Secure Hash Algorithm standards, published in 2015
+as https://csrc.nist.gov/pubs/fips/202/final[FIPS 202].
+
+SHA-3 includes 6 algorithms: SHA3-224, SHA3-256, SHA3-384, SHA3-512, SHAKE128, and SHAKE256.
+
+The SHA3 functions output a fixed-sized digest while SHAKE128 and SHAKE256 are approved extendable-output functions, also known as XOFs. XOFs permit generation
+of an arbitrarily long message digest in a defined manner.
+
+Unlike SHA-2, SHA3-224 is not a truncated version of the SHA3-256 algorithm. Instead, all SHA-3 algorithms create their digests by truncating the
+lower portion of the 1600-bit state permuted by the Keccak algorithm. The XOFs return their digests incrementally as fixed-sized blocks, using the truncation specified
+in Algorithm 8, step 8 of FIPS 202.
+
+SHA-3 uses 64 bit operations for all of the algorithms in the family.
+
 ### RIPEMD-160, RIPEMD-128
 
 Designed in 1996, https://en.wikipedia.org/wiki/RIPEMD[RIPEMD-160] is a cryptographic hash function that was less well known than MD5 and SHA-1,