If you use steganography with plaintext, you're relying on security by obscurity.
No. It is perfectly possible to have steganographic keys, in the same way that you have cryptographic keys.
Trivial example: If the key is 7, the hidden message can be extracted by combining the least significant bits of every 7th pixel of an image. (Incidentally, that hidden message could also be, and indeed probably should also be, encrypted.)
For an example that's only slightly more complex but might actually be useful, replace "7" with a seeded CSPRNG.
you're increasing the entropy of the plaintext message you're concealing it in.
Yes. But you should still be able to conceal a low-bitrate secret message inside a high-entropy covertext/envelope/whatever-you-call-it without a significant chance of being detected.
Trivial example: With a good algorithm and a stick full of 1MB JPEGs, it shouldn't be possible for an attacker to determine which files contain a concealed (140-byte) tweet and which don't.
No. It is perfectly possible to have steganographic keys, in the same way that you have cryptographic keys.
Trivial example: If the key is 7, the hidden message can be extracted by combining the least significant bits of every 7th pixel of an image. (Incidentally, that hidden message could also be, and indeed probably should also be, encrypted.)
For an example that's only slightly more complex but might actually be useful, replace "7" with a seeded CSPRNG.
you're increasing the entropy of the plaintext message you're concealing it in.
Yes. But you should still be able to conceal a low-bitrate secret message inside a high-entropy covertext/envelope/whatever-you-call-it without a significant chance of being detected.
Trivial example: With a good algorithm and a stick full of 1MB JPEGs, it shouldn't be possible for an attacker to determine which files contain a concealed (140-byte) tweet and which don't.