Hkdf.extract: def of bend-collections@1.0.0.0
Import: import bend-collections@1.0.0.0/spec/crypto/hkdf.bend as Hkdf
Lines 15-19 of bend-collections@1.0.0.0/spec/crypto/hkdf.bend: https://jend.leeeet.dev/read.txt?path=bend-collections@1.0.0.0/spec/crypto/hkdf.bend&start_line=15&end_line=19

import Base
import bend-collections@1.0.0.0/spec/crypto/hmac.bend as HMAC

# 2.2 Step 1: Extract. PRK = HMAC-Hash(salt, IKM). An absent salt is HashLen
# zero bytes; an empty salt gives the same HMAC key block (both are padded
# with zeros to the block size), so passing [] means "not provided".
def extract(+salt: List<&2, U32>, ikm: List<&2, U32>) -> List<&2, U32>:
  HMAC.hmac(salt, ikm)

Uses (3):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32
  https://jend.leeeet.dev/definition.txt?path=bend-collections@1.0.0.0/spec/crypto/hmac.bend&name=hmac