[aes/rtl] Rework naming and use of cipher operation signal
This commit changes the name of this signal from "mode" to "op"
(operation) and adds a separate "op" signal to the cipher core.
In AES terms, "mode" usually refers to the block cipher mode (e.g.
ECB, CBC, CTR) whereas "operation" refers to whether encryption
or decryption is performed. Depending on "mode" and "operation",
the actual cipher operation can either be "forward" or "inverse".
Signed-off-by: Pirmin Vogel <vogelpi@lowrisc.org>
diff --git a/hw/ip/aes/doc/_index.md b/hw/ip/aes/doc/_index.md
index 2651e3a..5b999e4 100644
--- a/hw/ip/aes/doc/_index.md
+++ b/hw/ip/aes/doc/_index.md
@@ -117,7 +117,7 @@
### Datapath Architecture and Operation
The AES unit implements the Equivalent Inverse Cipher described in the [AES specification](https://csrc.nist.gov/csrc/media/publications/fips/197/final/documents/fips-197.pdf).
-This allows for more efficient cipher data path sharing between encryption/decryption as the operations are applied in the same order (less muxes, simpler control), but requires the round key in decryption mode to be transformed using an inverse MixColumns in all rounds except for the first and the last one.
+This allows for more efficient cipher data path sharing between encryption/decryption as the operations are applied in the same order (less muxes, simpler control), but requires the round key during decryption to be transformed using an inverse MixColumns in all rounds except for the first and the last one.
This architectural choice targets at efficient cipher data path sharing and low area footprint.
Depending on the application scenario, other architectures might offer a more suitable area/performance tradeoff.
@@ -210,29 +210,29 @@
{{< wavejson >}}
{
signal: [
- { name: 'clk', wave: 'p........|.......'},
+ { name: 'clk', wave: 'p........|.......'},
['TL-UL IF',
- { name: 'write', wave: '01...0...|.......'},
- { name: 'addr', wave: 'x2345xxxx|xxxxxxx', data: 'K0 K1 K2 K3'},
- { name: 'wdata', wave: 'x2345xxxx|xxxxxxx', data: 'K0 K1 K2 K3'},
+ { name: 'write', wave: '01...0...|.......'},
+ { name: 'addr', wave: 'x2345xxxx|xxxxxxx', data: 'K0 K1 K2 K3'},
+ { name: 'wdata', wave: 'x2345xxxx|xxxxxxx', data: 'K0 K1 K2 K3'},
],
{},
['AES Unit',
- { name: 'Config mode', wave: 'x4...............', data: 'DECRYPT'},
- { name: 'AES mode', wave: '2........|.4.....', data: 'IDLE DECRYPT'},
- { name: 'KEM mode', wave: '2....3...|.4.....', data: 'IDLE ENCRYPT DECRYPT'},
- { name: 'round', wave: 'xxxxx2.22|22.2222', data: '0 1 2 9 0 1 2 3 4'},
- { name: 'key_init', wave: 'xxxx5....|.......', data: 'K0-3'},
- { name: 'key_full', wave: 'xxxxx5222|4.22222', data: 'K0-3 f(K) f(K) f(K) K0-3\' f(K) f(K) f(K) f(K) f(K)'},
- { name: 'key_dec', wave: 'xxxxxxxxx|4......', data: 'K0-3\''},
+ { name: 'Config op', wave: 'x4...............', data: 'DECRYPT'},
+ { name: 'AES op', wave: '2........|.4.....', data: 'IDLE DECRYPT'},
+ { name: 'KEM op', wave: '2....3...|.4.....', data: 'IDLE ENCRYPT DECRYPT'},
+ { name: 'round', wave: 'xxxxx2.22|22.2222', data: '0 1 2 9 0 1 2 3 4'},
+ { name: 'key_init', wave: 'xxxx5....|.......', data: 'K0-3'},
+ { name: 'key_full', wave: 'xxxxx5222|4.22222', data: 'K0-3 f(K) f(K) f(K) K0-3\' f(K) f(K) f(K) f(K) f(K)'},
+ { name: 'key_dec', wave: 'xxxxxxxxx|4......', data: 'K0-3\''},
]
]
}
{{< /wavejson >}}
-The AES unit is configured to do decryption (`Config mode` = DECRYPT).
-Once the new key has been provided via the control and status registers (top), this new key is loaded into the Full Key register (`key_full` = K0-3) and the KEM starts performing encryption (`KEM mode`=ENCRYPT).
-The cipher data path remains idle (`AES mode`=IDLE).
+The AES unit is configured to do decryption (`Config op` = DECRYPT).
+Once the new key has been provided via the control and status registers (top), this new key is loaded into the Full Key register (`key_full` = K0-3) and the KEM starts performing encryption (`KEM op`=ENCRYPT).
+The cipher data path remains idle (`AES op`=IDLE).
In every round, the value in `key_full` is updated.
After 10 encryption rounds, the value in `key_full` equals the start key for decryption.
This value is stored into the Decryption Key register (`key_dec` = K0-3' at the very bottom).
@@ -314,7 +314,7 @@
```c
// Enable autostart, disable overwriting of previous output data
REG32(AES_CTRL(0)) =
- mode << AES_CTRL_MODE |
+ op << AES_CTRL_OPERATION |
(key_len & AES_CTRL_KEY_LEN_MASK) << AES_CTRL_KEY_LEN_OFFSET |
0x0 << AES_CTRL_MANUAL_START_TRIGGER |
0x0 << AES_CTRL_FORCE_DATA_OVERWRITE;
