GASPER and LMD-GHOST in Blockchain Consensus Protocols
Gasper - Combining
GHOST & Casper
Presentation by Sarisht Wadhwa
Link to paper: https://arxiv.org/pdf/2003.03052.pdf
Asynchrony - Liveness and Termination
●
FLP Impossibility
https://groups.csail.mit.edu/tds/papers/Lynch/jacm85.pdf
Asynchrony - Liveness and Termination
●
FLP Impossibility
Two Ghosts in the same trench-coat
https://blog.ethereum.org/2020/02/12/validated-staking-on-eth2-2-two-ghosts-in-a-trench-coat/
I can solve
consensus with
liveness, but
can’t be safe
I can solve
consensus with
safety, but can’t
guarantee an
output each time
Two Ghosts in the same trench-coat
Ok Let’s
combine and do
it all**
Two Ghosts in the same trench-coat
Ideal View of live protocol
live
Ideal View of safe protocol
Something like PBFT suffices for a safe but non terminating consensus
safe
Organization of Presentation
➔
GHOST and its variants
➔
Casper FFG
➔
Gasper: Combining both the ghosts
GHOST
(And Variants)
Casper
FFG
GASPER
(GHOST+ CASPER FFG)
GHOST: Greediest Heaviest Observed SubTree
H
E
G
J
L
A
B
D
C
F
I
M
K
VIEW of Validator
LMD-GHOST:
Latest Message Driven GHOST
H
E
G
J
L
A
B
D
C
F
I
M
K
VIEW of Validator
H
E
G
J
L
A
B
D
C
F
I
M
K
VIEW of Validator
LMD-GHOST:
Latest Message Driven GHOST
GHOST Properties
Probabilistic
Safety
Always Live
Progress
LMD-GHOST
Casper
FFG
GASPER
(GHOST+ CASPER FFG)
GHOST
HLMD GHOST
Casper FFG
Checkpoint
Block A
Attestation
Justification
Justified
Checkpoint
Block A
Justified
Checkpoint
Block A
Casper FFG
Checkpoint
Block A
extends
Justified
Checkpoint
block B
Attestation
Justification
Extend the last justified block in your attestation
Casper FFG
Attestation
Justification
Checkpoint
Block B
Attestation
Justification
Checkpoint
Block A
extending B
Justified
Checkpoint
Block A
Casper FFG
Attestation
Justification
Checkpoint
Block B
Attestation
Justification
Checkpoint
Block A
extending B
Checkpoint
Block A
Casper FFG
Attestation
Justification
Checkpoint
Block B
Attestation
Justification
Checkpoint
Block A
extending B
Checkpoint
Block A
Slashing
Block A
Block B
height
Slashing
Block A
Block B
height
Slashing
Block A1
Block B1
Block A0
Block B0
Slashing
Block A1
Block B1
Block A0
Block B0
Casper FFG Properties
Accountable
Safety
Plausible
Liveness
Progress
LMD-GHOST
Slashing
GASPER
(GHOST+ CASPER FFG)
GHOST
HLMD-GHOST
Casper
FFG
Gasper
Epoch 0
Epoch 1
Epoch 2
Epoch 3
1
2
3
4
5
6
7
8
9
10
11
12
Epoch Boundary Blocks and Pairs
EBB - Epoch Boundary Block (Block, epoch)
LEBB - Last Epoch Boundary Block
Validators
Epoch 0
Epoch 1
Epoch 2
Epoch 3
1
2
3
4
5
6
7
8
9
10
11
12
Proposers
Validators
Epoch 0
Epoch 1
Epoch 2
Epoch 3
1
2
3
4
5
6
7
8
9
10
11
12
...
Committee
B
l
o
c
k
B
Blocks and attestations
A
t
t
e
s
t
a
t
i
o
n
A
Slot(B)
Parent(B)
Accepted attestations
Block Data
Slot(A)
Block(A)
Checkpoint Edge
Justification
k-Finalization
Progress
LMD-GHOST
Slashing
GASPER
(GHOST+ CASPER FFG)
GHOST
HLMD-GHOST
Casper
FFG
HLMD-GHOST:
Hybrid Latest Message Driven GHOST
H
E
G
J
L
A
B
D
C
F
I
M
K
VIEW of Validator
X
A’
B’
x10000
Justified
Block
Properties
●
O
n
e
e
p
o
c
h
-
>
A
t
-
m
o
s
t
o
n
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,
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(
⅓
)
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f
S
t
a
k
e
s
w
i
l
l
h
a
p
p
e
n
●
F
i
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a
l
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:
B
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!
M
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c
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h
a
p
p
e
n
i
n
t
h
i
s
c
a
s
e
.
GASPER Properties
Accountably
Safety
Always Live
Progress
LMD-GHOST
Slashing
GASPER
(GHOST+ CASPER FFG)
GHOST
HLMD-GHOST
Casper
FFG
Delve into the world of blockchain consensus with GASPER and LMD-GHOST, two innovative approaches combining safety and liveness properties. Learn about GHOST, Casper FFG, and the progress made in achieving probabilistic safety and liveness in distributed systems.
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Presentation Transcript
Gasper - Combining GHOST & Casper Presentation by Sarisht Wadhwa Link to paper: https://arxiv.org/pdf/2003.03052.pdf
Asynchrony - Liveness and Termination FLP Impossibility https://groups.csail.mit.edu/tds/papers/Lynch/jacm85.pdf
Asynchrony - Liveness and Termination FLP Impossibility But We want All!!
Two Ghosts in the same trench-coat I can solve consensus with safety, but can t guarantee an output each time I can solve consensus with liveness, but can t be safe https://blog.ethereum.org/2020/02/12/validated-staking-on-eth2-2-two-ghosts-in-a-trench-coat/
Two Ghosts in the same trench-coat Ok Let s combine and do it all**
Organization of Presentation GHOST and its variants GASPER (GHOST+ CASPER FFG) Casper FFG Gasper: Combining both the ghosts GHOST (And Variants) Casper FFG
GHOST: Greediest Heaviest Observed SubTree VIEW of Validator L D G J M A B I K F C H E
LMD-GHOST: Latest Message Driven GHOST VIEW of Validator L D G J M A B I K F C H E
LMD-GHOST: Latest Message Driven GHOST VIEW of Validator L D G J M A B I K F C H E
GHOST Properties Probabilistic Safety Always Live
Progress GASPER (GHOST+ CASPER FFG) HLMD GHOST Casper FFG LMD-GHOST GHOST
Casper FFG Attestation Justification Justified Checkpoint Block A Checkpoint Block A Justified Checkpoint Block A
Casper FFG Attestation Justification Checkpoint Block A extends Justified Checkpoint block B Extend the last justified block in your attestation
Casper FFG Attestation Justification Attestation Justification Justified Checkpoint Block A Checkpoint Block B Checkpoint Block A extending B
Casper FFG Attestation Justification Attestation Justification Checkpoint Block B Checkpoint Block A extending B Checkpoint Block A What if no 2/3 Majority is reached in this round?
Casper FFG Attestation Justification Attestation Justification Checkpoint Block B Checkpoint Block A extending B Checkpoint Block A
Slashing height Block A Block B
Slashing height Block A Block B Beacon Chain
Slashing Block A0 Block B0 Block B1 Block A1
Slashing Block A0 Block B0 Block B1 Block A1 Beacon Chain
Casper FFG Properties Plausible Liveness Accountable Safety
Progress GASPER (GHOST+ CASPER FFG) HLMD-GHOST LMD-GHOST Slashing Casper FFG GHOST
Gasper Epoch 3 Epoch 0 Epoch 1 Epoch 2 1 2 3 4 6 9 10 11 12 5 7 8
Epoch Boundary Blocks and Pairs EBB - Epoch Boundary Block (Block, epoch) LEBB - Last Epoch Boundary Block
Blocks and attestations Block B Attestation A Slot(B) Parent(B) Slot(A) Block(A) Checkpoint Edge Accepted attestations Block Data
Progress GASPER (GHOST+ CASPER FFG) HLMD-GHOST LMD-GHOST Slashing Casper FFG GHOST
HLMD-GHOST: Hybrid Latest Message Driven GHOST VIEW of Validator x10000 A B L D G J M X A B I K F C H E Justified Block
Properties One epoch -> At-most one Justification, or ( ) Slashing of Stakes will happen Finalization: Block always included, or system is broken! Major slashing can happen in this case.
GASPER Properties Accountably Safety Always Live
Progress GASPER (GHOST+ CASPER FFG) HLMD-GHOST LMD-GHOST Slashing Casper FFG GHOST
