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From: Rusty Russell <rusty@rustcorp.com.au>
To: "Jonas Schnelli" <dev@jonasschnelli.ch>
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Date: Tue, 28 Jun 2016 12:01:34 +0930
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Cc: bitcoin-dev@lists.linuxfoundation.org
Subject: [bitcoin-dev] BIP 151 use of HMAC_SHA512
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To quote:
> HMAC_SHA512(key=ecdh_secret|cipher-type,msg="encryption key").
>
> K_1 must be the left 32bytes of the HMAC_SHA512 hash.
> K_2 must be the right 32bytes of the HMAC_SHA512 hash.
This seems a weak reason to introduce SHA512 to the mix. Can we just
make:
K_1 = HMAC_SHA256(key=ecdh_secret|cipher-type,msg="header encryption key")
K_2 = HMAC_SHA256(key=ecdh_secret|cipher-type,msg="body encryption key")
Thanks,
Rusty.
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