Proof of work - Revision history

Atheros: updated for Protocol V3

2014-10-17T21:46:38Z

updated for Protocol V3

Atheros at 17:10, 3 May 2013

2013-05-03T17:10:49Z

Rwcarlsen: fixed trialVal definition

2013-04-06T18:10:03Z

fixed trialVal definition

Atheros at 20:27, 4 April 2013

2013-04-04T20:27:55Z

Atheros: Created page with "This page describes Bitmessage's Proof of work ("POW") mechanism as it currently exists. In this document, hash() means SHA512(). SHA512 was chosen as it is widely supported a..."

2013-04-04T20:14:11Z

Created page with "This page describes Bitmessage's Proof of work ("POW") mechanism as it currently exists. In this document, hash() means SHA512(). SHA512 was chosen as it is widely supported a..."

New page

This page describes Bitmessage's Proof of work ("POW") mechanism as it currently exists. In this document, hash() means SHA512(). SHA512 was chosen as it is widely supported and so that Bitcoin POW hardware cannot trivially be used for Bitmessage POWs. The author acknowledges that they are essentially the same algorithm with a different key size.

payloadLengthExtraBytes is a constant which equals 320

averageProofOfWorkNonceTrialsPerByte is a constant which equals 14000. The purpose of this value is to add some extra weight to small messages.

=== Do a POW ===

Let us use a msg message as an example.

payload = embeddedTime + encodedStreamNumber + encrypted

target = 2^64 / ((length of the payload in bytes + payloadLengthExtraBytes + 8) * averageProofOfWorkNonceTrialsPerByte)

initialHash = hash(payload)

start with trialValue = 99999999999999999999

also start with nonce = 0 where nonce is 8 bytes in length and can be hashed as if it is a string.

while trialValue > target:
nonce = nonce + 1
resultHash = hash(hash( nonce + initialHash ))
trialValue = the last 8 bytes of resultHash, converted to an integer

When this loop finishes, you will have your 8 byte nonce value which you can prepend onto the front of the payload. The message is then ready to send.

=== Check a POW ===

Let us assume that 'payload' contains the payload for a msg message (the nonce down through the encrypted message data).

nonce = the first 8 bytes of payload

dataToCheck = the ninth byte of payload on down (thus it is everything except the nonce)

initialHash = hash(dataToCheck)

resultHash = hash(hash( nonce + initialHash ))

POWValue = the first eight bytes of resultHash converted to an integer

target = 2^64 / ((length of payload + payloadLengthExtraBytes) * averageProofOfWorkNonceTrialsPerByte)

If POWValue is less than or equal to target, then the POW check passes.

@@ Line 1: / Line 1: @@
 This page describes Bitmessage's Proof of work ("POW") mechanism as it currently exists. In this document, hash() means SHA512(). SHA512 was chosen as it is widely supported and so that Bitcoin POW hardware cannot trivially be used for Bitmessage POWs. The author acknowledges that they are essentially the same algorithm with a different key size.
-averageProofOfWorkNonceTrialsPerByte is a constant which equals 320
+averageProofOfWorkNonceTrialsPerByte is set by the owner of a Bitmessage address. The default and minimum is 320. (This is the same as difficulty 1. If the difficulty is 2, then this value is 640).
-payloadLengthExtraBytes is a constant which equals 14000. The purpose of this value is to add some extra weight to small messages.
+payloadLengthExtraBytes is set by the owner of a Bitmessage address. The default and minimum is 14000. The purpose of this value is to add some extra weight to small messages. If the user sets the small message difficulty to 2, then this value is doubled.
 === Do a POW ===

@@ Line 1: / Line 1: @@
-This page describes Bitmessage's Proof of work ("POW") mechanism as it currently exists. In this document, hash() means SHA512(). SHA512 was chosen as it is widely supported and so that Bitcoin POW hardware cannot trivially be used for Bitmessage POWs. The author acknowledges that they are essentially the same algorithm with a different key size.
+This page describes Bitmessage's Proof of work ("POW") mechanism as it exists in Protocol Version 3. In this document, hash() means SHA512(). SHA512 was chosen as it is widely supported and so that Bitcoin POW hardware cannot trivially be used for Bitmessage POWs. The author acknowledges that they are essentially the same algorithm with a different key size.
-averageProofOfWorkNonceTrialsPerByte is set by the owner of a Bitmessage address. The default and minimum is 320. (This is the same as difficulty 1. If the difficulty is 2, then this value is 640).
+Both averageProofOfWorkNonceTrialsPerByte and payloadLengthExtraBytes are set by the owner of a Bitmessage address. The default and minimum for each is 1000. (This is the same as difficulty 1. If the difficulty is 2, then this value is 2000). The purpose of payloadLengthExtraBytes is to add some extra weight to small messages.
 === Do a POW ===
@@ Line 9: / Line 7: @@
 Let us use a msg message as an example.
-     payload = embeddedTime + encodedStreamNumber + encrypted
+     payload = embeddedTime + encodedObjectVersion + encodedStreamNumber + encrypted
-     target = 2^64 / ((length of the payload in bytes  +  payloadLengthExtraBytes + 8) * averageProofOfWorkNonceTrialsPerByte)
+     [[File:POW forumla 2.png|none|caption]]
      initialHash = hash(payload)
@@ Line 21: / Line 23: @@
      while trialValue > target:
          nonce = nonce + 1
-         resultHash = hash(hash( nonce + initialHash ))
+         resultHash = hash(hash( nonce || initialHash ))
          trialValue = the first 8 bytes of resultHash, converted to an integer
@@ Line 36: / Line 38: @@
      initialHash = hash(dataToCheck)
-     resultHash = hash(hash( nonce + initialHash ))
+     resultHash = hash(hash( nonce || initialHash ))
      POWValue = the first eight bytes of resultHash converted to an integer
-     target = 2^64 / ((length of payload  + payloadLengthExtraBytes) * averageProofOfWorkNonceTrialsPerByte)
+     TTL = the number of seconds in between now and the object expiresTime.
 If POWValue is less than or equal to target, then the POW check passes.