AES (aes-cbc-256) encryption/decryption with openssl expected output truncated - bash

Question

I wrote a script. Please pardon that I am not an expert in scripting.
Upon deciphering, the results gotten truncated.
[Message in text]: 0123456789abcdefghijklmnopqrstuvwxyz
message_input in hex: 303132333435363738396162636465666768696a6b6c6d6e6f707172737475767778797a0a
key: 788a1ca0bf1ab80f092841aabd77793f
hex string is too short, padding with zero bytes to length
c19f83afc1160ce81b0fc9906d513693386ccdd313b0f2884c698411441054e8
ciphered text: c19f83afc1160ce81b0fc9906d513693386ccdd313b0f2884c698411441054e8
IV: 7ecd3d63a8b74bb2f80d71a1c9d43359
deciphering ...
hex string is too short, padding with zero bytes to length
key: 788a1ca0bf1ab80f092841aabd77793f
iv: 7ecd3d63a8b74bb2f80d71a1c9d43359
answer: 30313233343536373839616263646566
Deciphered Message in hex: 30313233343536373839616263646566
deciphered text: 0123456789abcdef
The recovered deciphered text: 0123456789abcdef, ghijklmnopqrstuvwxyz gets truncated. This is supposed to be AES-CBC. Is there an option I did not turn on?
Here is the ciphering:
IV=$(openssl rand -hex 16)
get_key_for_ciphering; # key_for_ciphering gets populated
message_input=$(echo -n "${message_input//[[:space:]]/}") # remove spaces
echo "message_input in hex: "$message_input
echo "key": $key_for_ciphering;
ANS=$(echo "0: $message_input" | xxd -r | openssl enc -aes-256-cbc -iv $IV -K "$key_for_ciphering" | xxd -p)
ANS=$(echo -n "${ANS//[[:space:]]/}") # remove spaces
Here is the deciphering (message_input=$ANS):
get_key_for_ciphering; # key_for_ciphering gets populated
ANS=$(echo "0: $message_input" | xxd -r | openssl enc -aes-256-cbc -d -nopad -nosalt -K "$key_for_ciphering" -iv $IV | xxd -p) # -nopad -nosalt

Answer 1

Focusing in your question, the problem is in the xxd command. When converting a hex string to binary with xxd -r, you have to use the -p to tell xxd that is a plain hex string (no line breaks).
When converting back to hex with xxd -p, line breaks are added every 32 bytes. Unfortunately, xxd doesn't provide a flag to not include line breaks (you could use -c to set the number of columns, but it's limited to a max number). There are many option to remove line breaks, but one is appending a | tr -d '\n' to your command, as shown in the example below.
IV=$(openssl rand -hex 16)
key_for_ciphering=$(openssl rand -hex 16)
message_input="303132333435363738396162636465666768696a6b6c6d6e6f707172737475767778797a0a"
message_input=$(echo -n "${message_input//[[:space:]]/}") # remove spaces
echo "Message: $message_input"
echo "Key: $key_for_ciphering"
echo "IV: $IV"
ANS=$(echo "0: $message_input" | xxd -r -p | openssl enc -aes-256-cbc -iv $IV -K "$key_for_ciphering" | xxd -p | tr -d '\n')
ANS=$(echo -n "${ANS//[[:space:]]/}") # remove spaces
echo "Encrypted: $ANS"
ANS=$(echo "0: $ANS" | xxd -r -p | openssl enc -aes-256-cbc -d -nopad -nosalt -K "$key_for_ciphering" -iv $IV | xxd -p | tr -d '\n')
echo "Decrypted: $ANS"

Answer 2

---- Edit: ----
Doesn't work, as shell-parameters cannot contain binary zero. Possible fix with filters:
#!/bin/bash
tohex () {
perl -e 'binmode STDIN; while (<STDIN>) { print unpack "H*",$_; }'
}
fromhex () {
perl -e 'binmode STDIN; while (<STDIN>) { print pack "H*",$_; }'
}
binInput='0123456789abcdefghijklmnopqrstuvwxyz'
hexIV="$(openssl rand -hex 16)"
hexKey='788a1ca0bf1ab80f092841aabd77793f'
hexCipher="$(printf '%s' "$binInput" |\
openssl enc -aes-256-cbc -nosalt -iv "$hexIV" -K "$hexKey" | tohex)"
binResult="$(printf '%s' "$hexCipher" | fromhex |\
openssl enc -aes-256-cbc -d -iv "$hexIV" -K "$hexKey")"
if [ "$binInput" = "$binResult" ]; then echo OK;
fi
---- Original: ----
I think your problem lies in hexadecimal conversion. Try using perl pack/unpack:
tohex () {
perl -e 'print unpack "H*", "$ARGV[0]"' "$1"
}
fromhex () {
perl -e 'print pack "H*", "$ARGV[0]"' "$1"
}
message='0123456789abcdefghijklmnopqrstuvwxzy §"+!%/=()'
message_hex=$(tohex "$message")
message_cmp=$(fromhex "$message_hex")
if [ "$message" = "$message_cmp" ]; then echo OK; fi