Improve explanation of minSigPopPContext and DST in comments

Author: palas

cardano-api/src/Cardano/Api/Key/Internal/Leios.hs

@@ -190,10 +190,14 @@ blsPossessionProof hexBs =
     Left e -> error $ "blsPossessionProof: " ++ show e
     Right p -> p
 
--- | Proof-of-possession ciphersuite DST for the minimal-signature-size BLS12-381 variant.
+-- | Signing context including the Domain Separation Tag (DST) for the proofs-of-possession of
+-- BLS keys using the minimal-signature-size BLS12-381 variant.
 --
--- It is used when creating and verifying proofs of possession to ensure domain separation
--- between signing contexts.
+-- A Domain Separation Tag is a unique tag (like a magic number) that we add to ensure that
+-- the signature is used only in the context that it was intended for.
+-- This is because BLS keys and signatures can be used for multiple purposes, and
+-- we don't want a proof of possession for one purpose to be interpreted as something different
+-- in a different context.
 minSigPoPContext :: Crypto.BLS12381SignContext
 minSigPoPContext = Crypto.BLS12381SignContext (Just minSigPoPDST) Nothing