neil saitug niftynei

Blind Diffie-Hellman Key Exchange (blind ecash)

The goal of this protocol is for Bob to get Alice to perform a Diffie-Hellman key exchange blindly, such that when the unblinded value is returned, Alice recognizes it as her own, but can’t distinguish it from others (i.e. similar to a blind signature).

Alice:
A = a*G
return A

Bob:
Y = hash_to_curve(secret_message)
r = random blinding factor

Abstract

This proposal is an alternative to [bip119][] and [bip118][], providing the functionality of both proposals with minimal additional overhead in many cases, while clearing certain objections to both, and opening clear upgrade paths.

This is, in essence, an initially constrained version of Russel O'Connor's [OP_TXHASH+OP_CSFS proposal][].

	Latency Comparison Numbers (~2012)
	----------------------------------
	L1 cache reference 0.5 ns
	Branch mispredict 5 ns
	L2 cache reference 7 ns 14x L1 cache
	Mutex lock/unlock 25 ns
	Main memory reference 100 ns 20x L2 cache, 200x L1 cache
	Compress 1K bytes with Zippy 3,000 ns 3 us
	Send 1K bytes over 1 Gbps network 10,000 ns 10 us
	Read 4K randomly from SSD* 150,000 ns 150 us ~1GB/sec SSD

	passwd

	systemctl enable sshd.service
	systemctl start sshd.service

	parted -s /dev/sda mklabel gpt
	parted -s /dev/sda mkpart "primary" "fat16" "50MB" "60MB"
	parted -s /dev/sda mkpart "primary" "ext4" "1%" "99%"
	parted -s /dev/sda set 1 bios_grub on
	mkfs.ext4 /dev/sda2

	#
	# This is a scheme to encrypt a backup of a t-of-n Multisig spending script
	# such that any combination of t-of-n xpubkeys can recover the missing (n-t) xpubkeys.
	#
	#
	# In this example, we encrypt the 5 xpubkeys of a 3-of-5 Multisig
	# and demonstrate how to recover from any 3 xpubkeys the other 2 missing xpubkeys.
	#
	# The scheme is a simple variation of Shamir's secret sharing.
	# It is nicely compact. The encrypted payload is only the size of 2 xpubkeys.