Some BTC addresses start with a "3"

[OROBTC]

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When I have nothing better to do, I sometimes browse the blockchain via blockchain.info.  Really just to get a better feel for different kinds of transactions and to learn a bit more (some of you know I am a relative beginner who has pretty much had to "learn by doing" and not a programmer).

(Some time ago, I asked bitcointalk about addresses that have a small letter (after the 1) vs. a CAPITAL letter, and I also asked about how a small percentage of addresses have ONE less alphanumeric in their addresses vs. the overwhelming majority of others.  The answers I received explained BOTH points very well.  Thanks!)

Well, here is another little oddity I have seen recently.  A small percentage of addresses (maybe 0.5% -- one in 200 or 300 addresses) start with a 3.  One very interesting address that moves a LOT of BTC around (and starts with a 3) is at Block Height 342350 (won by Slush).  A LOT of BTC!

There are only some 93 transactions at 342350, so if you want to see for yourself, just drop by and scroll down.  That "3" address is the only one I saw there.

Why is it that some addresses start with a 3?

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I guess that a second question is in order.  Is posting a public address (like the one starting with "3" at 342350) considered "Bad Form" here at bitcointalk? 

Hey, I don't want to cause any trouble around here...

[ranochigo]

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When I have nothing better to do, I sometimes browse the blockchain via blockchain.info.  Really just to get a better feel for different kinds of transactions and to learn a bit more (some of you know I am a relative beginner who has pretty much had to "learn by doing" and not a programmer).

(Some time ago, I asked bitcointalk about addresses that have a small letter (after the 1) vs. a CAPITAL letter, and I also asked about how a small percentage of addresses have ONE less alphanumeric in their addresses vs. the overwhelming majority of others.  The answers I received explained BOTH points very well.  Thanks!)

Well, here is another little oddity I have seen recently.  A small percentage of addresses (maybe 0.5% -- one in 200 or 300 addresses) start with a 3.  One very interesting address that moves a LOT of BTC around (and starts with a 3) is at Block Height 342350 (won by Slush).  A LOT of BTC!

There are only some 93 transactions at 342350, so if you want to see for yourself, just drop by and scroll down.  That "3" address is the only one I saw there.

Why is it that some addresses start with a 3?

*  *  *

I guess that a second question is in order.  Is posting a public address (like the one starting with "3" at 342350) considered "Bad Form" here at bitcointalk?  

Hey, I don't want to cause any trouble around here...

Address starting with 3 is a multisignature address, a address requiring 2-of-3 signatures to be able to be spent. It is an address associated with more than one ECDSA private key. It is usually used as cold storage as it is harder for one to steal 2 private keys compared to 1. It can also be a protection against malware as you could keep the keys on separate computers. Keeping one of the three keys safety is also a good practice, if one of the keys is lost, the bitcoin can still be spent using 2 of the remaining keys. It can also be shared between multiple people, majority of the people can vote and spend the coin.

[pedrog]

Multi-signature addresses

Addresses can be created that require a combination of multiple private keys. Since these take advantage of newer features, they begin with the newer prefix of 3 instead of the older 1. These can be thought of as the equivalent of writing a check to two parties - "pay to the order of somebody AND somebody else" - where both parties must endorse the check in order to receive the funds.

The actual requirement (number of private keys needed, their corresponding public keys, etc.) that must be satisfied to spend the funds is decided in advance by the person generating this type of address, and once an address is created, the requirement cannot be changed without generating a new address.


https://en.bitcoin.it/wiki/Address#Multi-signature_addresses

[cheekychap]

Like others said its a multisig address .Other addresses start with 1.
I saw it the first time, I signed up for Bit-x. Thought they had it that ways somehow.

[OROBTC]

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ranochigo, pedrog, and cheekychap

Thank you, one can learn something every day!  

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What about posting "interesting looking" addresses?  Is that considered "Bad Form" (publicizing someone's public key just so I can get a question answered)?

[doof]

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ranochigo, pedrog, and cheekychap

Thank you, one can learn something every day!  

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What about posting "interesting looking" addresses?  Is that considered "Bad Form" (publicizing someone's public key just so I can get a question answered)?

Every address is public knowledge.  Associating it with an individual could be considered poor form.

[tonygal]

Hmm, are you guys sure that there is such a strict distinction between the two?
I was aware that your usual one-man-address starts with 1 and your usual
multisig address with 3. But to my knowledge a 3-address can also be a regular
onesig address, although an unusual one.

[hhanh00]

Hmm, are you guys sure that there is such a strict distinction between the two?
I was aware that your usual one-man-address starts with 1 and your usual
multisig address with 3. But to my knowledge a 3-address can also be a regular
onesig address, although an unusual one.

3-address are pay-to-script-hash addresses (P2SH in short). Most of the time they are used to do multisig but they are not limited to that. You probably saw one that does something different. Alternatively, you can also do multisig without a 3-address. It is rare but possible.

[pitham1]

Aah.....
I always wondered why the addresses in BitX started with 3.
Now that makes sense.

[cryptworld]

they are multisignature adresses! now bitstamp uses that type of adresses

[dsly]

they are multisignature adresses! now bitstamp uses that type of adresses

Does that guarantee that they wont lose funds ever again ?

[redsn0w]

they are multisignature adresses! now bitstamp uses that type of adresses

Also TheRockTrading, it uses greenAddress ( multiSign +2FA + instant confirm -if the other user uses also greenaddress as wallet).

[tonygal]

Hmm, are you guys sure that there is such a strict distinction between the two?
I was aware that your usual one-man-address starts with 1 and your usual
multisig address with 3. But to my knowledge a 3-address can also be a regular
onesig address, although an unusual one.

3-address are pay-to-script-hash addresses (P2SH in short). Most of the time they are used to do multisig but they are not limited to that. You probably saw one that does something different. Alternatively, you can also do multisig without a 3-address. It is rare but possible.

Thanks, hhanh00. That seems to be the ultimate answer: 1... is public key hash while 3... is pay to script hash, see
https://en.bitcoin.it/wiki/Pay_to_script_hash
An explanation like

they are multisignature adresses!

is thus an oversimplification in my eyes.

[pooya87]

it starts either with 1 or 3 and interesting enough the first example on https://en.bitcoin.it/wiki/Address is this one "3J98t1WpEZ73CNmQviecrnyiWrnqRhWNLy" which starts with 3 which is associated with the new features

[OROBTC]

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pooya87

That bitcoin/wiki link explains a lot, thank you!

Highly recommended for these BTC address questions.

[doggieTattoo]

they are multisignature adresses! now bitstamp uses that type of adresses

Does that guarantee that they wont lose funds ever again ?

No. If an attacker were to have at least two of the private keys associated with bitstamp's mltisig address(es) then they could steal their funds, although it would be less likely that an attacker would be able to do so.

As mentioned many times above an address starting with a 3 is a multisg address

[Bitcoinexp]

Well, you will find that the exchange in my signature does use multi-sig addresses and currently uses addresses that start with a "3". Case solved.

[ranochigo]

they are multisignature adresses! now bitstamp uses that type of adresses

Does that guarantee that they wont lose funds ever again ?

No. If an attacker were to have at least two of the private keys associated with bitstamp's mltisig address(es) then they could steal their funds, although it would be less likely that an attacker would be able to do so.

As mentioned many times above an address starting with a 3 is a multisg address

That scenario is highly unlikely to happen. If a attacker gain access to the server, the attacker would only gain access to one of the key. To steal the funds, the attacker would have to go through bitgo's check. If invalidated, the attack will fail. Technically this is safe if done right. Eg. Keeping the third key safe in case anything happens.

[pereira4]

Interesting. My friend was in Bit-x and told me about the 3 thing. It was really weird, I thought it was some sort of altcoin.

[micheline]

I've learned something new today.

Thanks to the thread starter for asking this question.

Address starting with 3 is a multisignature address, a address requiring 2-of-3 signatures to be able to be spent. It is an address associated with more than one ECDSA private key. It is usually used as cold storage as it is harder for one to steal 2 private keys compared to 1. It can also be a protection against malware as you could keep the keys on separate computers. Keeping one of the three keys safety is also a good practice, if one of the keys is lost, the bitcoin can still be spent using 2 of the remaining keys. It can also be shared between multiple people, majority of the people can vote and spend the coin.

That is really useful. I've already asked myself if it would be possible to "split" the key for security reasons and have some kind of fallback in case I loose one part. Great to see that a solution exists already.