Quote

Blockstream's explorer can already show the signature of each input

I don't want to get only (r,s) pair, because it is trivial. I want to get data, behind a given z-value.

For example, you can see this transaction:

Code:

01000000000102fff7f7881a8099afa6940d42d1e7f6362bec38171ea3edf433541db4e4ad969f0000000000eeffffffef51e1b804cc89d182d279655c3aa89e815b1b309fe287d9b2b55d57b90ec68a0100000000ffffffff02202cb206000000001976a9148280b37df378db99f66f85c95a783a76ac7a6d5988ac9093510d000000001976a9143bde42dbee7e4dbe6a21b2d50ce2f0167faa815988ac000147304402203609e17b84f6a7d30c80bfa610b5b4542f32a8a0d5447a12fb1366d7f01cc44a0220573a954c4518331561406f90300e8f3358f51928d43c212a8caed02de67eebee0111000000

And then, you can easily notice this signature:

Code:

47304402203609e17b84f6a7d30c80bfa610b5b4542f32a8a0d5447a12fb1366d7f01cc44a0220573a954c4518331561406f90300e8f3358f51928d43c212a8caed02de67eebee01

Then, extracting (r,s) pair is trivial, and anyone can do that easily:

Code:

r=3609e17b84f6a7d30c80bfa610b5b4542f32a8a0d5447a12fb1366d7f01cc44a
s=573a954c4518331561406f90300e8f3358f51928d43c212a8caed02de67eebee

However, to fully verify things, you also need z-value. And it is not just a transaction hash. Instead, it is that thing:

Code:

0100000096b827c8483d4e9b96712b6713a7b68d6e8003a781feba36c31143470b4efd3752b0a642eea2fb7ae638c36f6252b6750293dbe574a806984b8e4d8548339a3bef51e1b804cc89d182d279655c3aa89e815b1b309fe287d9b2b55d57b90ec68a010000001976a9141d0f172a0ecb48aee1be1f2687d2963ae33f71a188ac0046c32300000000ffffffff863ef3e1a92afbfdb97f31ad0fc7683ee943e9abcf2501590ff8f6551f47e5e51100000001000000

And then, you can complete the proof:

Code:

z=c37af31116d1b27caf68aae9e3ac82f1477929014d5b917657d0eb49478cb670
r=3609e17b84f6a7d30c80bfa610b5b4542f32a8a0d5447a12fb1366d7f01cc44a
s=573a954c4518331561406f90300e8f3358f51928d43c212a8caed02de67eebee
Q=025476c2e83188368da1ff3e292e7acafcdb3566bb0ad253f62fc70f07aeee6357
n=fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141
1/s=18c3acadca5e7b9fc3cd6b221f30e66fa26c07450aeafe2327f6c51fd7a75147
z/s=df8e03f52bb441d2e9ed959efabceaebbc9211918c5e5420b8164577f9c603eb
r/s=93978dc15dbb351e107f083839792787230beb342db2a8bea4fd3fa18990c6a7
(z/s)G=024D008960C8AAFA40869FDACF9088FC96F68E6AC6DBC26ADAB611145C7BB2C12A
(r/s)Q=03E830824028F11FC59B3D4C1A7A135D1DFB3FD3CA7E7563D896889B46A77DCF13
R=(z/s)G+(r/s)Q
R=023609E17B84F6A7D30C80BFA610B5B4542F32A8A0D5447A12FB1366D7F01CC44A
R.x=3609e17b84f6a7d30c80bfa610b5b4542f32a8a0d5447a12fb1366d7f01cc44a

But: getting this z-value is far from trivial. And it is different, if you have different address types. It is not just a hash of the transaction, it is much more complex. For example: https://github.com/bitcoin/bips/blob/master/bip-0143.mediawiki

So, is there any tool, which would work in that way?

Code:

decodesignatures 01000000000102fff7f7881a8099afa6940d42d1e7f6362bec38171ea3edf433541db4e4ad969f0000000000eeffffffef51e1b804cc89d182d279655c3aa89e815b1b309fe287d9b2b55d57b90ec68a0100000000ffffffff02202cb206000000001976a9148280b37df378db99f66f85c95a783a76ac7a6d5988ac9093510d000000001976a9143bde42dbee7e4dbe6a21b2d50ce2f0167faa815988ac000147304402203609e17b84f6a7d30c80bfa610b5b4542f32a8a0d5447a12fb1366d7f01cc44a0220573a954c4518331561406f90300e8f3358f51928d43c212a8caed02de67eebee0111000000
{
"signatures": [
{
"hex": "47304402203609e17b84f6a7d30c80bfa610b5b4542f32a8a0d5447a12fb1366d7f01cc44a0220573a954c4518331561406f90300e8f3358f51928d43c212a8caed02de67eebee01",
"r": "3609e17b84f6a7d30c80bfa610b5b4542f32a8a0d5447a12fb1366d7f01cc44a",
"s": "573a954c4518331561406f90300e8f3358f51928d43c212a8caed02de67eebee",
"sighash": "01",
"data": "0100000096b827c8483d4e9b96712b6713a7b68d6e8003a781feba36c31143470b4efd3752b0a642eea2fb7ae638c36f6252b6750293dbe574a806984b8e4d8548339a3bef51e1b804cc89d182d279655c3aa89e815b1b309fe287d9b2b55d57b90ec68a010000001976a9141d0f172a0ecb48aee1be1f2687d2963ae33f71a188ac0046c32300000000ffffffff863ef3e1a92afbfdb97f31ad0fc7683ee943e9abcf2501590ff8f6551f47e5e51100000001000000",
"z": "c37af31116d1b27caf68aae9e3ac82f1477929014d5b917657d0eb49478cb670",
"version": 1,
"prevouts": [
"hex": "96b827c8483d4e9b96712b6713a7b68d6e8003a781feba36c31143470b4efd37",
"data": "fff7f7881a8099afa6940d42d1e7f6362bec38171ea3edf433541db4e4ad969f00000000ef51e1b804cc89d182d279655c3aa89e815b1b309fe287d9b2b55d57b90ec68a01000000",
"vin": [
{
"txid": "fff7f7881a8099afa6940d42d1e7f6362bec38171ea3edf433541db4e4ad969f",
"vout": 0
},
{
"txid": "ef51e1b804cc89d182d279655c3aa89e815b1b309fe287d9b2b55d57b90ec68a",
"vout": 1
}
]
],
"sequence": [
"hex": "52b0a642eea2fb7ae638c36f6252b6750293dbe574a806984b8e4d8548339a3b",
"data": "eeffffffffffffff",
"sequences": [
4294967278,
4294967295
]
]
"vin": [
{
"txid": "ef51e1b804cc89d182d279655c3aa89e815b1b309fe287d9b2b55d57b90ec68a",
"vout": 1,
"scriptSig": {
"hex": "1976a9141d0f172a0ecb48aee1be1f2687d2963ae33f71a188ac"
},
"value": 6.00000000,
"sequence": 4294967295
}
],
"outputs": "863ef3e1a92afbfdb97f31ad0fc7683ee943e9abcf2501590ff8f6551f47e5e5",
"locktime": 17,
"sighash": "01000000"
}
]
}

Quote

the explorer has to store this additional data on top of what they are storing

They don't have to "store" it, just "compute" and "show to the user". And if this is computationally expensive, then maybe it can be done on a client side, instead of server side?