Taking the hash of the secret would then require an extra step to make sure
the hash is valid for secp256k1.

Using the x value directly avoids the need for that check.

On Fri, Apr 24, 2015 at 10:35 PM, Patrick Mccorry (PGR) <
patrick.mccorry@newcastle.ac.uk> wrote:

>  When computing the diffie Hellman secret - why do you choose the x
> co-ordinate instead of the hash of the secret which is standard practice
> for stealth addresses
>
> Sent from my iPhone
>
> On 24 Apr 2015, at 21:27, Justus Ranvier <justus.ranvier@monetas.net>
> wrote:
>
>   -----BEGIN PGP SIGNED MESSAGE-----
>
> Hash: SHA1
>
>
>
> https://github.com/justusranvier/rfc/blob/payment_code/bips/bip-pc01.mediawiki
>
>
>  This link contains an RFC for a new type of Bitcoin address called a
> "payment code"
>
>
>  Payment codes are SPV-friendly alternatives to DarkWallet-style stealth
> addresses which provide useful features such as positively identifying
> senders to recipients and automatically providing for transaction refunds.
>
>
>  Payment codes can be publicly advertised and associated with a real-life
> identity without causing a loss of financial privacy.
>
>
>  Compared to stealth addresses, payment codes require less blockchain
> data storage.
>
>
>  Payment codes require 65 bytes of OP_RETURN data per sender-recipient
> pair, while stealth addresses require 40 bytes per transaction.
>
>
>  -----BEGIN PGP SIGNATURE-----
>
> Version: GnuPG v1
>
>
>  iQIcBAEBAgAGBQJVOqCRAAoJECpf2nDq2eYjluEP/RVJk+miDIihY4ilIvUbKvMd
>
> JLLqHr7Q1dlZyMIG/UqVWdoP5hzg/16B+q2iAB9jXozPnrDp0mggBh6rIGroevAa
>
> Kqfrs+Rrog1w9auhd67LWORDqav6YIrjTJIxdLxe11IEiq5rWbHPNUEDMzdEmHbz
>
> QfTH7KWAP2BasO5ETXcfu6BcccrXZ3XOKLON2h3NGD/cEDizY+uT2k3QN54z+KxG
>
> NB9scKbzVvsJwkyBrgbV+As9H3k6PnFsojYgAaE9gkp7D2+ahjzUiOH5rv6TbbYR
>
> o2X5MOiTY2/YZEqZPG7IR03ZAgeLVCvXXysjPOfzUKbmTF4w849sm8BuhixzDXHo
>
> 2V/HHKoGclIohcODBCWi0tVQXshZt4QkCNJBW5o3nL6Nn2YOp6hmw8YKAHnw3E7h
>
> /wIgk5f+NOLl/iIxoAxAdavEj5P6N4ic+OB6MAjnhEilWfBvCIpqWLGNvrtOhEa9
>
> EnPHcgb4ILBu4OionJhsNpJ/O95C0OEypMm25MIS+rQcV4Uxe5IOS2OuT/GreLET
>
> n/7Y0mJbqYbLBjVsfS+DNjvsgyJl5AxhcMrdVyXJjSYVcCoRhcoX5Ceidd+YkbHI
>
> OMs5f63tM1Rgi/WY4Ct80SD5EbULZuu8j1KJ9HPGuMt081JSBH+L5isiKuazPeO+
>
> SGApMBd4Q89fKzL2djae
>
> =Dypr
>
> -----END PGP SIGNATURE-----
>
>
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