External access to these functions was removed in RustCrypto#304 when the old
`internals` module and `expose-internals` feature were removed. There
are some valid use cases for them, though (see RustCrypto#351), so let's bring
back a subset of what was in `internals` using the same naming and
documentation conventions that the aes crate uses for its hazardous
functions.

Much of the added or changed documentation is derived from that in aes.

Fixes RustCrypto#351.

External access to these functions was removed in #304 when the old
`internals` module and `expose-internals` feature were removed. There
are some valid use cases for them, though (see #351), so let's bring
back a subset of what was in `internals` using the same naming and
documentation conventions that the aes crate uses for its hazardous
functions.

Much of the added or changed documentation is derived from that in
the `aes` crate.

Fixes #351.

In versions of the rsa crate >= 0.9 the
`generate_multi_prime_key_with_exp` functions are no longer public.
Their reasons for doing so are here:
RustCrypto/RSA#304 but the TLDR; is: so no one
hurts themselves.

The closest analog available is `RsaPrivateKey::new_with_exp` but it
doesn't allow us to specify the number of primes. Internally it hard
codes this value to '2' which is our current default. None of our
example configs set this value and they probably shouldn't so this
commit removes the `num-primes` config option from the RsaKeyConfig.

This changes the config file structure so this commit bumps the version
number too.

In versions of the rsa crate >= 0.9 the
`generate_multi_prime_key_with_exp` functions are no longer public.
Their reasons for doing so are here:
RustCrypto/RSA#304 but the TLDR; is: so no one
hurts themselves.

The closest analog available is `RsaPrivateKey::new_with_exp` but it
doesn't allow us to specify the number of primes. Internally it hard
codes this value to '2' which is our current default. None of our
example configs set this value and they probably shouldn't so this
commit removes the `num-primes` config option from the RsaKeyConfig.

This changes the config file structure so this commit bumps the version
number too.

* feat: decouple key generation and random generation

Make generate_multi_prime_key_with_exp() generic enough to generate
abstract key structure. Rewrite RsaPrivateKey constructors to use
RsaPrivateKey::from_components().

* feat: move key-related traits to separate module

Move PublicKeyParts to the separate module.

* feat: stop using RsaPrivateKey in internals.rs

Make internals.rs generic enough to be moved to the algorithms module.

* feat: move soft RSA implementation to crate::algorithms::rsa.rs

Separate software RSA implementation to separate module under
crate::algorithms.

* key: drop raw_int_*_primitive wrappers

Now as raw_int_encryption_primitive() and raw_int_decryption_primitive()
became simple wrappers around properly defined functions we can inline
them and always use software RSA algorithm from src::algorithms::rsa.rs.

* feat: move internals.rs to src/algortihms/pad.rs

internals.rs now contains only small functions related to BigUint to
Vec<u8> conversion. Move them to src/algorithms/pad.rs and get rid of
internals.rs

* algorithms: protect all functions with pub(crate)

While it is expected that the functions inside algorithms crates might
be useful (and used) by other parties, they are low level functions and
as such impose a high risk of being misused. Protect all of them with
pub(crate) to prevent them from being exposed by mistake.

Also add big fat warnings to raw RSA functions, which should never be
used unless authors knows exactly what they are using.

Signed-off-by: Dmitry Baryshkov <[email protected]>

…pto#352)

External access to these functions was removed in RustCrypto#304 when the old
`internals` module and `expose-internals` feature were removed. There
are some valid use cases for them, though (see RustCrypto#351), so let's bring
back a subset of what was in `internals` using the same naming and
documentation conventions that the aes crate uses for its hazardous
functions.

Much of the added or changed documentation is derived from that in
the `aes` crate.

Fixes RustCrypto#351.