todos.txt

#####################################
### Issues / errors in processing ###
#####################################
### https://github.com/davit-gh/ecommerce ?
#####################################


I42: 16nov2016, svn:
====================
make a copy of wallet and priv keys from SuSE cold and from Mac Bitcoin client into new virtual machine, to see that copying of wallets works well ...


I43: 20dec2016, svn:
====================
tcls_create.sh: 
### TX_IN: call STEP 3-7 ###
...
# if only prev_TX is given, we could fetch remaining items with 'get_trx_values' ?
--> assume we have -f and -t, then we can read values from network?   


I45: 26dec2016, svn:
====================
tcls_sign.sh
add some testcases based on priv keys from file "Address_Generation_Test.txt" in the Bitcoin directory. The file contains priv and pub keys ... 


I46: 04jan2017, svn:
====================
Can I build a transaction review of prev trx? The tree looks like this (left to right):

prev trx      TRX2          TRX1       my wallet
=================================================
Input 1 \
Input 2 ----- UTXO --\
Input 3 /             \
                       ---- UTX0 ----> 1JBM...68m 
                      /
Input 4 ----- UTXO --/


I47: 20mar2017, svn:
====================
beautify output of tcls_tx2txt.sh: similiar to the way, the tree output is done in the "dot profile" alias:
alias tree="find ./ -print | sed -e 's;[^/]*/; /;g;s;/ ;    ;g;s;^ /$;.;;s; /;|-- ;g'"


I49: 27mar2017, svn:
====================
maybe an idea for the future:
A high level algorithm for processing payments on a website via RPC/cli

Say, I'll have a python script. Do I understand correctly, that I'll have to call these:
1) getnewaddress
2) getreceivedbyaddress
That is, I won't need the "gettransaction" and "listreceivedbyaddress" calls.

---> no, for a webpage with an address it is better to use HD wallets: 
Hierarchical Deterministic Wallets (BIP0032/BIP0044)
q: how many public/private keypairs can a 24 word hierarchical deterministic wallet produce?
a: 2^31, the number of words in the mnemonic has nothing to do with the capacity, it just adjusts the entropy for the key derivation


I56: 23jun2017, svn, tcls_sign.sh:
=================================
when a tx has more than 100 utxo, the signing process creates an error roughly every 2nd attempt.
Looks like this happens for signatures, where a new S-Value must be calculated. The new S-value should be less then N/2. The system creates a new S value, but it's length is then 63 bytes, instead of 64 bytes.
Approach: create a raw tx, and sign it 10 times, and see the values for R and S?


I58: 20jul2017, svn:
====================
P2SH scripts - length limitations:
https://bitcoin.stackexchange.com/questions/38937/what-was-the-original-rationale-for-limiting-the-maximum-push-size


I61: tcls_testcases for OP_RETURN
=================================
https://blockchain.info/tx/52dd20f60d6e14e5a783e7668cf410efdea40cd9a92479b0f2423d0bc63575fa?format=hex
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

https://blockchain.info/tx/728e24b2e7dd137e574c433a8db08ac2aa0bf0588ad7716e4c5a7da45dbb5933?format=hex
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

https://blockchain.info/tx/d276abe15791941649c3ca8425d79167cc1cf801f83aa99753fe7f42740c0f23?format=hex
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


I63: tcls_create.sh - only partially done
===================
when in Africa, the curl call cannot go through. See:
https://bitcoin.stackexchange.com/questions/60296/getting-current-bitcoin-fees-from-command-line
include a switch that goes around usage of bitcoinfees.21.co and set a default value? 
or look at johoenicke: https://dedi.jochen-hoenicke.de/queue/more/#24h
or use this as approximation for size, and multiply with a satoshi/byte:
compressed pubkey, tx size =   a*148 + b*34 + 10 +/- 1
uncompressed pubkey, tx size = a*180 + b*34 + 10 +/- 1
also SegWit:
============
... how to figure out how much transaction size is allocated to witness data? 
vbytes are calculated by first dividing just the size of the witness data by 4 and then adding that to the size of the non-witness data.
see also I66 and I73.


I64: tcls_create.sh
===================
possible extension/thoughts for cold storage:
Create multi-sig wallet offline

Goal: Never expose private keys to the internet, and have a dead man's switch
Goal: If any two people lose access to their devices or die simultaneously, access to the coins is not lost
Goal: If one person loses their key, is a victim of theft or goes rouge, the coins are not lost.

    Setup a server that holds the private key I wrote down on paper.
    Discard the paper I wrote the private key to.
    Instruct the server to listen from pings with a certain signature and count the time since the last ping.
    Run an application every time I start my computer that pings the server.
    Instruct the server to sms me a warning if it has not been pinged for 1 month.
    Instruct the server to sms me the private key if it has not been pinged for 2 month.
    Instruct the server to sms the truster persons the private key if it has not been pinged for 3 month.


I65: 10min tx:
==============
based on an article here:
https://www.reddit.com/r/Bitcoin/comments/3yulwv/any_examples_of_the_10_minute_script_thats_a/
this tx can knock down nodes...
what about mine? It is in the file "tcls_10min_tx.txt"


I66: bitcoin fees:
==================
As for formulas, if you use standard addresses (not P2SH), the formula is:

fee = (n_inputs * 148 + n_outputs * 34 + 10) * price_per_byte

SegWit slightly changes this, where instead of paying per byte, you pay per unit of weight: 1 byte of non witness data = 4 weight, 1 byte of witness data = 1 weight. 
see also I63 and I73.

I67b: signature for P2SH:
========================
is this realized correctly in tcls_sign.sh?
https://bitcoin.stackexchange.com/questions/60468/signature-scheme-for-p2sh


I68: signature for signing...
==============================
is this realized correctly in tcls_sign.sh?
https://bitcoin.stackexchange.com/questions/57848/how-to-tell-which-part-of-the-previous-tx-i-need-to-make-the-hash-to-sign-for-an/57866#57866


I70: Multisig & Segwit:
=======================
integrate contents of file "160905_Multisig_Segwit.txt" into tx_cl_suite


I71: Smart Contract:
====================
ermöglicht Bitcoin, eine Schwelle der täglichen Auszahlung festzulegen, und erst wenn diese überschritten wird, muss eine Transaktion von einer zweiten Partei signiert werden?

--> ALL|ANYONECANPAY
This construction can be used to make a “crowdfunding”-style transaction. Someone attempting to raise funds can construct a transaction with a single out‐ put. The single output pays the “goal” amount to the fundraiser. Such a transac‐ tion is obviously not valid, as it has no inputs. However, others can now amend it by adding an input of their own, as a donation. They sign their own input with ALL|ANYONECANPAY. Unless enough inputs are gathered to reach the value of the output, the transaction is invalid. Each donation is a “pledge,” which cannot be collected by the fundraiser until the entire goal amount is raised.


I73a: tcls_sign.sh 
==================
this script sig should have 48 at the beginning?
4930450220494D2C9E461CEE7F8F31B294C479535C991CED8B8AA47C05D7A26A9A7B9E818E022100A5625FF149EAC1505160ACC5CEFAF3DD978C8A8370F1DEEBEFD3772AE1E00D7801
--> sig length is 142chars, 71 Bytes (without SIGHASH_ALL), hex 0x47
--> add SIGHASH_ALL, length is 72 Bytes, hex 0x48

Playing with OpenSSL, when changing this line:
   echo "ScriptSig: "
   echo 30480220494D2C9E461...
to
   echo 30270220494D2C9E461...
the openssl utility would accept the signature anyways... at least on the Mac.
What are the implications? 


I73b: tcls_create.sh
====================
when creating a multisig tx with redeem scripts, need to calculate tx fees better.
when redeemscript is given, decompose redeemscript (tcls_in_sig_script.sh), and 
add 0x47, 0x48 or 0x49 (71,72 or 73 decimal) bytes. Take the average for each sig. 
A multisig is normally n-of-m, so for each 'n' in each input (TX_IN) add 72 Bytes.
compressed pubkey, tx size =   a*148 + b*34 + 10 +/- 1
uncompressed pubkey, tx size = a*180 + b*34 + 10 +/- 1
also SegWit:
============
... how to figure out how much transaction size is allocated to witness data? 
vbytes are calculated by first dividing just the size of the witness data by 4 and then adding that to the size of the non-witness data.
see also I66.


I74: SegWit / Part II :-)
=========================
how to integrate SEGWIT details:
https://bitcoincore.org/en/segwit_wallet_dev/


I76: 28nov2017, svn, CLTV or CSV
=================================
A      can sign anytime
B,C,D  can sign in a 2of3 multisig
E,F    can sign in a two of two multisig 

OP_IF
  pubA OP_CHECKSIG
OP_ELSE
  OP_2 pubB pubC pubD OP_6 OP_CHECKMULTISIGVERIFY
  OP_2 pubE pubF OP_2 OP_CHECKMULTISIG
OP_ENDIF

and now bring in CSV or CLTV ! How?


I77: 02dec2017, svn, sigscript
===============================
tcls_in_sig_script.sh: needs to work with testnet addresses!
when running with testnet addresses, worng addresses are displayed.
See testcase "tcls_testcases_create.sh -l 11" and webpage https://people.xiph.org/~greg/escrowexample.txt
testcase 11a is ok (create a tx), testcase 11b is technically ok, but tcls_tx2txt.sh calls 
tcls_in_sig_script.sh, and this interprets addresses incorrectly.


I78: 03dec2017, svn:
====================
awk scripts to check for length and characters:
can the awk script be replaced? (tcls_verify_hexkey.awk, tcls_verify_bc_address.awk)
tcls_create.sh: see line ~190 in procedure chk_tx_ID:
--> if [ -z "${utxo_TX_ID##*[![:xdigit:]]*}" ] ; then ...


I79: 03dec2017, svn:
====================
tcls_create.sh: can a tx with many outputs be created? 
there are no testcases to produce a tx with many outputs?
and then create a testcase in the TESTCASE 4 section, which rejects tx, if the sum of input values < sum of output values


I80: 03dec2017, svn:
====================
https://bitcoin.stackexchange.com/questions/66197/step-by-step-example-to-redeem-a-p2sh-output-required
can this be verified in create/sign?


I81: 31dec2017, svn:
====================
Segwit, see answer by MeshCollider in this stackexchange question:
https://bitcoin.stackexchange.com/questions/65404/calculate-segwit-address-from-public-address/65470?noredirect=1#comment77749_65470


I82, 11Jan2018, svn:
====================
smart contract: can this be done?
https://bitcointalk.org/index.php?topic=2723908.0


I83, 15Feb2018, svn - tcls_tx2txt.sh
====================================
decoding of scripts in thsi tx with many segwit bc1 addresses does not work - howto?
https://blockchain.info/de/tx/6e58d8c695e3e42c5a7807e2ed99ad7f7731658dfb0d62cdfef44dad8964b350
https://bitcointalk.org/index.php?topic=2664728.0


I84, 25Feb2018, svn - tcls_verify_sig.sh
=========================================
How can this program verify a tx of the blockchain? 
--> it would need to de-assemble a tx, get its double hash, along with sig, pubkey.
For the signatures: without length parameter and without "Sighash_All"?


I85: 07mar2018, svn, tcls_in_sig_script.sh, line 346:
=====================================================
#####################################
### STATUS 0a (s0a_SIG_LEN)       ###
### THIS CODE SEEMS TO BE REDUNDANT ###
### It is called from mainloop with ###
### opcode "3C" ? This is not sig ? ###
#####################################
s0a_SIG_LEN() 
--> is it old code? not used anymore? Why would "3C" be signature?


I86: 08mar2018, svn, tcls_strict_sig_verify.sh:
===============================================
verify code to sig checking. 
look here: http://bitcoin-development.narkive.com/OOU2XVSG/bitcoin-development-who-is-creating-non-der-signatures
* R and S are signed integers, encoded as a big-endian byte sequence.
They are stored in as few bytes as possible (i.e., no 0x00 padding in
front), except that a single 0x00 byte is needed and even required
when the byte following it has its highest bit set, to prevent it
from being interpreted as a negative number.

--> so, only if highest bit is 1, then zero pad?


I87: 14mar2018, svn, tcls_in_sig_script.sh
==========================================
https://bitcoin.stackexchange.com/questions/72471/getrawtransaction-asm-returns-with-all-should-it-be/72484#72484
correction of displayed signatures, as per Pieter's comment:
It's strange to prefix all those things with "OP_". They're not opcodes; just part of the DER serialization. And the sighash ALL flag is appended by Bitcoin to the ECDSA signature; it's not part of it, and certainly not DER encoded. – Pieter Wuille yesterday 

yup, sure. Got that, no Op_Codes, maybe operators, or TT for type tags. In the ASN1 specs they talk a lot about byte values, maybe BV instead. – pebwindkraft yesterday   


I88: 15Apr2018, svn, tcls_s2u.sh:
=================================
if the tx has many inputs, how will the scriptSigs/pubkeys be displayed? 
Currently, when more than one input is involved, the program sets values to hex 0x00.
need a second loop to present the double hash with signature[n] and pubkey[n] ...


I89: 15May2018, svn, tcls_key2pem:
==================================
is this useful for implementation?
https://bitcoin.stackexchange.com/questions/59644/how-do-these-openssl-commands-create-a-bitcoin-private-key-from-a-ecdsa-keypair/59646#59646
look at all comments sections...



I90: 05Jun2018, svn, SegWit:
============================
https://blockchain.info/rawtx/497e90946be5ac4076497476c221d5165549e45040700d06f0b10091e2f144d5
this tx is not correctly displayed at the end with the witness data - the index counters always start at 0. Also the input script parts are not decoded ("220020...") 
./tcls_tx2txt.sh -vv -t 497e90946be5ac4076497476c221d5165549e45040700d06f0b10091e2f144d5 



I91: 05Jun2018, svn, SegWit:
============================
see, if the answer from Mike D can be integrated in the picture "keys.png":
https://bitcoin.stackexchange.com/questions/75910/how-to-generate-a-native-segwit-address-and-p2sh-segwit-address-from-a-standard


I92: 10Jul2018, svn, signature verification:
============================================
Verify a P2SH tx signature with OpenSSL at the command line?
In the case of a P2SH tx, I don't have a public key. I have a redeemscript. 
Do I need to extract the pubkey, and use it?
In case of MultiSig: which pubkey?



I93: 10Jul2018, svn, tcls_p2sh_sc.sh:
=====================================
https://bitcointalk.org/index.php?topic=4641339.0
--> creterawtransaction und das "data" keyword!

I94: 01Nov2018, svn, tcls_out_pk_script.sh:
===========================================
This script on testnet provides wrong data, decoding shows:
  TX_OUT[0] pk_script (uchar[])
  01022103341B4D862E7E1C3D7FE7D0ADE7E97DFAC122760B1EF4FFB21B7A9A27DD525B6C2102EE1C79ACEE56F0E2CAFCC1069A6E1E1E9D059FF9A60B60904E97A455D5B27F672102839D639C109F090104EAB7C3EEF07D6BF25952A5A88C65BC5B185F0EA2A3FAF20103AE
    21: OP_Data33
        03341B4D862E7E1C:3D7FE7D0ADE7E97D
        FAC122760B1EF4FF:B21B7A9A27DD525B
        6C
    21: unknown opcode 
   21: OP_Data33
        02839D639C109F09:0104EAB7C3EEF07D
        6BF25952A5A88C65:BC5B185F0EA2A3FA
        F2
    01: unknown opcode 
   03341B4D862E7E1C3D7FE7D0ADE7E97DFAC122760B1EF4FFB21B7A9A27DD525B6C02839D639C109F090104EAB7C3EEF07D6BF25952A5A88C65BC5B185F0EA2A3FAF2

where it should be something like this?
    01: Push next byte as data onto stack
        02
    21: OP_Data33
        03341B4D862E7E1C:3D7FE7D0ADE7E97D
        FAC122760B1EF4FF:B21B7A9A27DD525B
        6C
    21: OP_Data33
        02EE1C79ACEE56F0:E2CAFCC1069A6E1E
        1E9D059FF9A60B60:904E97A455D5B27F
        67
    21: OP_Data33
        02839D639C109F09:0104EAB7C3EEF07D
        6BF25952A5A88C65:BC5B185F0EA2A3FA 
        F2
    01: Push next byte as data onto stack
        03
    AE: OP_CHECKMULTISIG

same for this:
./tcls_out_pk_script.sh 0102210378D430274F8C5EC1321338151E9F27F4C676A008BDF8638D07C0B6BE9AB35C712102B568858A407A8721923B89DF9963D30013639AC690CCE5F555529B77B83CBFC721034DA006F958BEBA78EC54443DF4A3F52237253F7AE8CBDB17DCCF3FEAA57F31260103AE

Hint: ./tcls_in_sig_script.sh decodes correctly !

and this one as well:
53B275A914F45D94733D430261962932E0C847075195916A0487
   53: OP_3
    B2: unknown opcode 
   A9: OP_HASH160
    14: OP_Data14 (= decimal 20)
        F45D94733D430261:962932E0C8470751
        95916A04
    87: OP_EQUAL
  This is a P2SH script:
   -p2sh F45D94733D430261962932E0C847075195916A04

Hint: ./tcls_in_sig_script.sh decodes correctly !




#####################################
### Extensions / new Requirements ###
#####################################

E2: MultiSig
===============
For important values: make use of a 2of3 multisig with one in cold storage
generate 3 addresses (and 3 private keys) A, B & C... and 
create 1 multisig address (D) using those 3 in a 2-of-3 configuration

the multisig address starts with a "3", all the others (A,B & C) should be "1". 
send funds into the multisig address D (starts with a "3")... 
make sure all the private keys for your A, B & C addresses are all backed up/stored independently of each other. 
to take funds out of D, create a transaction using one of A,B or C.. and then co-sign the transaction using one of the other addresses.

file:///Data/BitCoin/Bitcoin_multisig_the_hard_way_P2SH.html


E3: Sending
===============
can a signed trx be sent to the net without tools?
--> https://bitcointalk.org/index.php?topic=1043518.0
curl -X POST -d tx=010000000158891e8f28100642464417f53845c3953a43e31b35d061bdbf6ca3a64fffabb8000000008c493046022100a9d501a6f59c45a24e65e5030903cfd80ba33910f24d6a505961d64fa5042b4f02210089fa7cc00ab2b5fc15499fa259a057e6d0911d4e849f1720cc6bc58e941fe7e20141041a2756dd506e45a1142c7f7f03ae9d3d9954f8543f4c3ca56f025df66f1afcba6086cec8d4135cbb5f5f1d731f25ba0884fc06945c9bbf69b9b543ca91866e79ffffffff01204e0000000000001976a914d04b020dab70a7dd7055db3bbc70d27c1b25a99c88ac00000000 https://blockchain.info/pushtx
also:
https://github.com/laanwj/bitcoin-submittx


E4: creating priv/pub keypairs
===============================
create a priv/pubkey pair using arcrandom on OpenBSD?
similiar to "bitcoin_tools.sh" ?


E5: Steganography
=================
http://incoherency.co.uk/blog/stories/steganographic-bitcoin-seeds.html


E6: BIP39
=========
https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki

   #!/bin/sh
   echo " "
   echo "create a 128 bits (64 bytes) sample string: "
   echo "random" | openssl dgst -sha256
   
   echo "check the length, must be 64"
   printf "87c1b129fbadd7b6e9abc0a9ef7695436d767aece042bec198a97e949fcbe14c" | wc -c
   
   echo "convert into a hex file to prepare sha256"
   printf $( echo "87c1b129fbadd7b6e9abc0a9ef7695436d767aece042bec198a97e949fcbe14c" | sed 's/[[:xdigit:]]\{2\}/\\x&/g') > tmp_file.hex
   
   echo "verify hex file content"
   hexdump -C tmp_file.hex
   
   echo "do a sha256 on it, and take first Byte"
   openssl dgst -sha256 <tmp_file.hex 
   
   echo "get first byte"
   openssl dgst -sha256 <tmp_file.hex | cut -c 10,11
   
   echo "concatenate to hex string, and check length=264 bits (33 bytes, 66 chars)"
   printf "87C1B129FBADD7B6E9ABC0A9EF7695436D767AECE042BEC198A97E949FCBE14C0D" | wc -c
   
   # convert hex to binary string 
   echo "obase=2;ibase=16;87C1B129FBADD7B6E9ABC0A9EF7695436D767AECE042BEC198A97E949FCBE14C0D" | bc
   # this results in this string:
   # 10000111110000011011000100101001111110111010110111010111101101101110
   # 10011010101111000000101010011110111101110110100101010100001101101101
   # 01110110011110101110110011100000010000101011111011000001100110001010
   # 100101111110100101001001111111001011111000010100110000001101
   
   # loop every 11th char throug the string, and lookup the word
     offset=10
     from=1
     to=$offset
   
     echo "bits         dec + 1=line    --> word"
     echo "                (+ 1 cause file starts with line number 1)"
     echo "====         ============================================="
     while [ $to -le 256 ] 
      do
       to=$(( $from + $offset ))
       word11bits=$( printf "100001111100000110110001001010011111101110101101110101111011011011101001101010111100000010101001111011110111011010010101010000110110110101110110011110101110110011100000010000101011111011000001100110001010100101111110100101001001111111001011111000010100110000001101" | cut -b $from-$to )
       word_num=$( echo "ibase=2;$word11bits" | bc ) 
       word_line=$(( word_num + 1 ))
       word=$( sed -n ${word_line}p bip39_words.txt )
       printf "%11s %4s + 1=%4s %11s \n" $word11bits $word_num $word_line $word
       from=$(( $to + 1 ))
     done
   
   echo " "
   echo "############################ and now backwards ############################"
   echo " "
   
   printf "bits          dec    <-- word \n" 
   # loop every 11th char throug the string, and lookup the word
   # for word in march assault engine warrior talent swarm pluck job prepare knife pipe man student dice receive analyst salute art clean wood enemy tourist lunch like
     for word in fold useful mirror diagram search fade gloom verify tonight april oyster lens pluck milk domain venue crawl charge face orchard render either route fat
      do
       line=$( grep -n ^$word$ bip39_words.txt | cut -d: -f1 )
       # line=$(( $line - 1 ))
       word_bits=$( echo "obase=2;$line" | bc )
       printf "%11s %5s %11s \n" $word_bits $line $word
     done
   
   
   echo " "
   echo "filling up the spaces with '0' reveals this:"
   echo "1000011111000001101100010010100111111011101011011101011110110110111010011010101111000000"
   echo "1010100111101111011101101001010101000011011011010111011001111010111011001110000001000010"
   echo "1011111011000001100110001010100101111110100101001001111111001011111000010100110000001101"
   
   echo " "
   echo "converting line by line to hex:"
   bitstr1=$( echo "obase=16;ibase=2;0101101010111110000000100011011010011110100011000010001010100011110110001110011110010110" | bc )
   bitstr2=$( echo "obase=16;ibase=2;1110010010100001011000100111101001000000001010100110110100011001010100000100011110010100" | bc )
   bitstr3=$( echo "obase=16;ibase=2;0011001011000100110101010100011011001110000110110110001010001110011011110010101010011100" | bc )
   echo $bitstr1
   echo $bitstr2
   echo $bitstr3
   
   echo " "
   echo "concatenated to a single hex value:"
   printf "%s%s%s\n" $bitstr1 $bitstr2 $bitstr3
   echo " "
   echo "original 32bytes/64chars string was:"
   echo "87c1b129fbadd7b6e9abc0a9ef7695436d767aece042bec198a97e949fcbe14c" 
   echo " "
   echo " "
   
   
   
E7: SEGWIT
==========
a:) be able to read and decode segwit tx
b:) make the "wallet" segwit compliant:
https://bitcoincore.org/en/segwit_wallet_dev/


E8: Lightning:
==============
Check out some of the testnet lightning wallets and applications:
1) HTLC.me web wallet ( https://htlc.me/ )
2) Eclair testnet android wallet ( Google Play Store )
3) Lightning Desktop App ( https://github.com/lightninglabs/lightning-app/releases )
4) yalls.org for spending testnet microtransactions ( https://yalls.org/ )


E9: base58 validations:
=======================
https://github.com/bitcoin/bitcoin/blob/master/src/test/data/base58_keys_valid.json


E10: Cold Storage:
==================
Large-cap cold storage would have to have some of the following.

- Address limit. Each address must have no more than X amount of bitcoins. This is basic risk management and limits the losses from a single stolen/lost address.

- Timelock. This makes it impossible for someone to steal your bitcoins even when you are tortured and tell them every detail, at least until the timelock expires.

- Multisig. Generate two separate keys, A and B. Each key has an associated seed. Store your bitcoins in a 2-of-2 multisig address and store the seed phrases in physically separate, secure locations. Note that you lose control of your coins if you lose *either* key, so you need to make sure that your backup situation is set up appropriately