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Update cipher light -> block cipher definition

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Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
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Manuel Pégourié-Gonnard 2023-12-07 12:12:39 +01:00
parent 303121eb16
commit b8c4254f44
1 changed files with 21 additions and 37 deletions
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58
docs/architecture/psa-migration/md-cipher-dispatch.md
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@ -379,6 +379,8 @@ Those costs could be avoided by refactoring (parts of) Cipher, but that would pr
- significant differences in how the `cipher.h` API is implemented between builds with the full Cipher or only a subset;
- or more work to apply the simplifications to all of Cipher.
Prototyping both approaches showed better code size savings and cleaner code with a new internal module.
## Specification
### MD light
@ -564,50 +566,32 @@ The architecture can be extended to support `MBEDTLS_PSA_CRYPTO_CLIENT` with a l
* Compile-time dependencies: instead of checking `defined(MBEDTLS_PSA_CRYPTO_C)`, check `defined(MBEDTLS_PSA_CRYPTO_C) || defined(MBEDTLS_PSA_CRYPTO_CLIENT)`.
* Implementers of `MBEDTLS_PSA_CRYPTO_CLIENT` will need to provide `psa_can_do_hash()` (or a more general function `psa_can_do`) alongside `psa_crypto_init()`. Note that at this point, it will become a public interface, hence we won't be able to change it at a whim.
### Cipher light
### Internal "block cipher" abstraction (Cipher light)
#### Definition
**Note:** this definition is tentative an may be refined when implementing and
testing, based and what's needed by internal users of Cipher light. The new
config symbol will not be considered public so its definition may change.
The new module is automatically enabled in `build_info.h` by modules that need
it, namely: CCM, GCM, only when `CIPHER_C` is not available. Note: CCM and GCM
currently depend on the full `CIPHER_C` (enforced by `check_config.h`); this
hard dependency would be replaced by the above auto-enablement.
Cipher light will be automatically enabled in `build_info.h` by modules that
need it, namely: CCM, GCM. Note: CCM and GCM currently depend on the full
`CIPHER_C` (enforced by `check_config.h`); this hard dependency would be
replaced by the above auto-enablement.
Cipher light includes:
- some info functions;
- support for block ciphers in ECB mode, encrypt only (note: in Cipher, "ECB"
means just one block, contrary to PSA);
- part of the streaming API for unauthenticated ciphers;
- only AES, Aria and Camellia.
This excludes:
- the one-shot API for unauthenticated ciphers;
- the AEAD/KW API (both one-shot and streaming);
- support for stream ciphers;
- support for other modes of block ciphers (CBC, CTR, CFB, etc.);
- DES and variants (3DES).
The following API functions, and supporting types, are candidates for
inclusion in the Cipher light API, with limited features as above:
The following API functions are offered:
```
mbedtls_cipher_info_from_values
mbedtls_cipher_info_get_block_size
mbedtls_cipher_init
mbedtls_cipher_setup
mbedtls_cipher_setkey
mbedtls_cipher_free
mbedtls_cipher_update
void mbedtls_block_cipher_init(mbedtls_block_cipher_context_t *ctx);
void mbedtls_block_cipher_free(mbedtls_block_cipher_context_t *ctx);
int mbedtls_block_cipher_setup(mbedtls_block_cipher_context_t *ctx,
mbedtls_cipher_id_t cipher_id);
int mbedtls_block_cipher_setkey(mbedtls_block_cipher_context_t *ctx,
const unsigned char *key,
unsigned key_bitlen);
int mbedtls_block_cipher_encrypt(mbedtls_block_cipher_context_t *ctx,
const unsigned char input[16],
unsigned char output[16]);
```
Note: `mbedtls_cipher_info_get_block_size()` can be hard-coded to return 16,
as all three supported block ciphers have the same block size (DES was
excluded).
The only supported ciphers are AES, ARIA and Camellia. They are identified by
an `mbedtls_cipher_id_t` in the `setup()` function, because that's how they're
identifed by callers (GCM/CCM).
#### Cipher light dual dispatch