diff --git a/BSP.markdown b/BSP.markdown
index 601a91b..ac04fe9 100644
--- a/BSP.markdown
+++ b/BSP.markdown
@@ -14,6 +14,8 @@ BSP uses a cryptographic hash function, H(m), with an output length of HASH_LEN
 
 * `HASH(x_1, ..., x_n) == H(len(x_1) || x_1 || ... || len(x_n) || x_n)`
 
+> Implementation note: We propose to use BLAKE2s as the hash function, which gives HASH_LEN = 32.
+
 ### Channel identifiers
 
 Each channel has a unique identifier HASH_LEN bytes long. This identifier is supplied by the client and is not interpreted by BSP, but to prevent collisions between clients, BSP specifies how channel identifiers may be generated. The channel identifier may be random: