How can I convert a SHA256 hash into a Bitcoin base58 private key?

Question

How can I take the output of sha256sum

sudofox@ubuntu:~$ echo -n 'Hi guys!' | sha256sum
7542fb6685f9fd8f37d56faf62f0bb4563684a51539e4b26f0840db361e0027c  -

and turn it into a Base58Check encoded private key?

I need to be able to do this with a list of SHA256 keys. Is there a script I can download, or must I spend a few weeks making it just so I can make my temporary addresses?

In response to first comment: No, I must input a string, like "fluttershy", for example, into sha256sum and then I must encode the output of sha256sum into a base58check private key.

string -->sha256sum --> some automagic process, which is the purpose of this question --> bitcoin private key.

Update: For anyone wanting to use Grondilu's Bitcoin Bash Tools: You need to source the bitcoin.sh file after extracting it into your directory to use the functions.

source ./bitcoin.sh

Update 2 (Aug 2017): Rewrote script to go from step 1 to WIF in one go. You can just add the declaration of base58 and the encodeBase58 functions from bitcoin.sh if you want to skip the rest of the lib.

#!/bin/bash
#Tool to convert bitcoin privkeys into WIF keys
# by sudofox

source ./bitcoin.sh

KEY=$1 # first arg

# add 0x80 to beginning
EXTENDEDKEY=$(echo 80$KEY)
FIRSTHASH=$(echo -n "$EXTENDEDKEY" |xxd -r -p |sha256sum -b|awk '{print $1}')
SECONDHASH=$(echo -n "$FIRSTHASH" |xxd -r -p |sha256sum -b|awk '{print $1}')
CHECKSUM=$(echo $SECONDHASH|cut -c1-8)
FINAL=$(encodeBase58 $EXTENDEDKEY$CHECKSUM)
echo $FINAL

The usage would be

./sha256_to_privkey.sh key

where in my example (see Stephen Gornick's answer), key would be

807542FB6685F9FD8F37D56FAF62F0BB4563684A51539E4B26F0840DB361E0027CCD5C4A8E

Do the same thing for the various functions, modifying as needed. Hope this helps anyone struggling to use the tools.

Answer 1

What you are requesting is described as computing the Wallet Import Format for that private key:

• http://en.bitcoin.it/wiki/Wallet_import_format

Using your example:

1.) Take a private key (Below is the HEX representation of binary value)

7542FB6685F9FD8F37D56FAF62F0BB4563684A51539E4B26F0840DB361E0027C

2.) Add a 0x80 byte in front of it

807542FB6685F9FD8F37D56FAF62F0BB4563684A51539E4B26F0840DB361E0027C

3.) Perform SHA-256 hash on the extended key

$ echo -n '807542FB6685F9FD8F37D56FAF62F0BB4563684A51539E4B26F0840DB361E0027C' | xxd -r -p | sha256sum -b

7DE4708EB23AB611371BB778FC0C8BDE80394AB2D8704D7129FB5771E2F1730D

4.) Perform SHA-256 hash on result of SHA-256 hash

$ echo -n '7DE4708EB23AB611371BB778FC0C8BDE80394AB2D8704D7129FB5771E2F1730D' | xxd -r -p | sha256sum -b

CD5C4A8E03DFBB0E3AA021C2D74A9EAA43CE4C9CB1B20FC88729A7A5834141CA

5.) Take the first 4 bytes of the second SHA-256 hash, this is the checksum

CD5C4A8E

6.) Add the 4 checksum bytes from point 5 at the end of the extended key from point 2

807542FB6685F9FD8F37D56FAF62F0BB4563684A51539E4B26F0840DB361E0027CCD5C4A8E

7.) Convert the result from a byte string into Base58 to get it into the Base58Check format. This is also known as the Wallet Import Format

(Converted from point 6 to base58 using https://bitcointools.appspot.com, or using encodeBase58 from https://github.com/grondilu/bitcoin-bash-tools)

5JhvsapkHeHjy2FiUQYwXh1d74evuMd3rGcKGnifCdFR5G8e6nH