Base64 output looks unfamiliar enough that it is easy to mistake it for encrypted text. It is not. Base64 is a reversible representation that makes binary data easier to carry through systems designed around text.
Why Base64 exists
Many protocols and text formats were historically safer when data used a limited set of printable characters. Base64 takes bytes and represents them using letters, digits and a small number of symbols. Any compatible decoder can reverse that representation without a password or key.
A tiny example
The text hello becomes aGVsbG8=. Nothing secret happened. If you paste that string into a Base64 decoder, you get hello back immediately.
Where it is useful
You will see Base64 in email attachments, data URLs, API payloads, certificates and configuration formats. It is useful when a system needs to move binary or arbitrary byte sequences through a text-safe channel.
Why files get bigger
Base64 uses more characters than the original binary representation. As a rule of thumb, encoded data is roughly one-third larger before any surrounding markup. It is therefore a poor choice when your only goal is compression.
Do not hide passwords with Base64
If a secret is merely Base64-encoded, anyone who can read it can decode it. Protection requires an appropriate cryptographic system with keys and a threat model—not cosmetic transformation.
Watch text encoding when results look wrong
Base64 operates on bytes. テキスト first has to be represented in a character encoding such as UTF-8. If two systems disagree about that encoding, decoded non-ASCII characters can look corrupted even though the Base64 itself is valid.
When decoding unknown content
Treat the result as untrusted data. Decoding a string is generally harmless, but opening an unknown decoded file or executing decoded script content can be risky. Inspect first, especially when the input came from an untrusted source.
Base64 is valuable precisely because it is simple and reversible. Use it for representation and transport; use real security controls for confidentiality.