encrypt string with openssl to send via email or chat

openssl genrsa -out key.pem
openssl rsa -in key.pem -pubout -out key.pub

Now you'll have pub + private keys
You can send the pub key to supplying user, who can then encrypt with it, and you can decrypt

To encrypt:

echo "xxxxxxxx" | openssl rsautl -encrypt -inkey ./key.pub -pubin | base64

To decrypt:

echo "my_b64_string==" | base64 -d | openssl rsautl -decrypt -inkey key.pem