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Date: Mon, 22 Jul 2013 16:44:59 +0200
From: Pieter Wuille <pieter.wuille@gmail.com>
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Subject: [Bitcoin-development] [RFC] Standard for private keys with birth
	timestamp
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Hello,

I should have brought up this suggestion before, as there seems to be relevant other work.

I'd like to propose encoding keys data (whatever type) with a birth timestamp as:
 * <serialized key>@<unix timestamp in decimal>

The reason for not incorporating this inside the key serialization (for example BIP32), is because
birth timestamps are more generally a property of an address, rather than the key it is derived from.
For one, it is useful for non-extended standard serialized private keys, but for P2SH addresses,
the "private key" is really the actual scriptPubKey, but birth data is equally useful for this.

Reason for choosing the '@' character: it's not present in the base58, hex, or base64 encodings that
are typically used for key/script data.

One downside is that this means no checksum-protection for the timestamp, but the advantage is
increased genericity. It's also longer than using a binary encoding, but this is an optional
part anyway, and I think "human typing" is already fairly hard anyway.

-- 
Pieter