Bitcoin Forum

Hey!

I was just wondering why all bitcoin addresses start with a "1".

Thanks.

Because at a certain step durring address generation a "version byte" is added in front of the hash. IIRC its
VersionByte + RIPEMD-160(sha256(PubKey). Thus at this stage the address starts with 00 (in hex) for the main bitcoin network. Then there is the checksum which is the first 4 bytes of sha256(sha256(VersionByte+RIPEMD-160(sha256(PubKey)))) that gets attached to the end. This does not influence the beginning however, thus we still have 00 (still in hex). The last step is the Base58 encoding, which has no zero. Thus the first value is a 1 and the 00 get converted to 1something.

They don't ALL start with a 1.

Pay-to-ScriptHash addresses (commonly used for multi-sig) start with a 3.

Bitcoin Addresses have three parts.

The first part is a one byte "version" that indicates what type of output script the address represents.  The most commonly used output script (Pay-to-PubKeyHash) uses a "version" of 0x00

The second part is the hash.  In the case of a Pay-to-ScriptHash address, this would be the 20 byte hash of the script.  In the more common Pay-to_PubKeyHash address, this would be a 20 byte hash of the ECDSA public key.

The last part is a 4 byte checksum calculated as the first 4 bytes of a 32 byte SHA-256 hash.  This is used to verify that there weren't any typing errors when entering the bitcoin address and prevents accidentally sending to a mis-typed address.

Once all 25 bytes are concatenated together, the resulting value is converted to base58 using the following value representations:

Value	Character	Value	Character	Value	Character	Value	Character
0	1	1	2	2	3	3	4
4	5	5	6	6	7	7	8
8	9	9	A	10	B	11	C
12	D	13	E	14	F	15	G
16	H	17	J	18	K	19	L
20	M	21	N	22	P	23	Q
24	R	25	S	26	T	27	U
28	V	29	W	30	X	31	Y
32	Z	33	a	34	b	35	c
36	d	37	e	38	f	39	g
40	h	41	i	42	j	43	k
44	m	45	n	46	o	47	p
48	q	49	r	50	s	51	t
52	u	53	v	54	w	55	x
56	y	57	z

The leading character '1', which has a value of zero in base58, is reserved for representing an entire leading zero byte, as when it is in a leading position, has no value as a base-58 symbol. There can be one or more leading '1's when necessary to represent one or more leading zero bytes.

because it was 1st crypto!

If an address begin with "1" then it's a hash of a public key, "3" for a script hash, "5" for a private uncompressed key, etc

https://en.bitcoin.it/wiki/List_of_address_prefixes (https://en.bitcoin.it/wiki/List_of_address_prefixes)

Ummm, im not really sure what all of these technical terms are...

From what I understand, its because thats the version number?

tl;dr yes, but only for the "usual" addresses (pay 2 pubkeyhash)

By looking the combination address , I think it need a very long time.

But is there any chance that someday bitcoin address will run out of address ?

No.

The identifying part of a bitcoin address is a 160-bit hash, 160 bits gives in the range of 10^48 addresses, or roughly 1 for every atom on the planet

Lol how the hell do you guys remember all this stuff ?

Remember what stuff?