AES - AES Accelerator#

Advanced Encryption Standard Accelerator (AES) Peripheral API.

This module contains functions to control the AES peripheral of Silicon Labs 32-bit MCUs and SoCs.

The AES peripheral supports AES block cipher encryption and decryption with 128 bit and 256 bit keys. The following block cipher modes are supported:

CBC - Cipher Block Chaining mode
CFB - Cipher Feedback mode
CTR - Counter mode
ECB - Electronic Code Book mode
OFB - Output Feedback mode

The following input/output notations should be noted:

Input/output data (plaintext, ciphertext, key, and so on) are treated as byte arrays, starting with the most significant byte, i.e., 32 bytes of plaintext (B0...B31) is located in memory in the same order, with B0 at the lower address and B31 at the higher address.

Byte arrays must always be a multiple of AES block size, i.e., a multiple of 16. Padding, if required, is done at the end of the byte array.

Byte arrays should be word (32 bit) aligned for performance considerations, since the array is accessed with a 32 bit access type. Cortex-M supports unaligned accesses with a performance penalty.

It is possible to specify the same output buffer as an input buffer as long as they point to the same address. In that case, the provided input buffer is replaced with the encrypted/decrypted output. Notice that buffers must be exactly overlapping. If partly overlapping, the behavior is undefined.

Use a cipher mode according to its requirements to avoid breaking security. See a specific cipher mode theory for details.

References:

Wikipedia - Cipher modes, http://en.wikipedia.org/wiki/Cipher_modes

Recommendation for Block Cipher Modes of Operation, NIST Special Publication 800-38A, 2001 Edition, http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf

The following example shows how to perform an AES-128 CBC encryption:

Enable clocks:

/* AES is a HFCORECLK peripheral */
CMU_ClockEnable(cmuClock_AES, true);

Execute AES-128 CBC encryption:

/* Encrypt a plaintext message (64 bytes) using the AES CBC block cipher mode with a 128 bits key and initial vector (iv) of 16 bytes.  */
const uint8_t plaintext[64] = { 0x6B, 0xC1, 0xBE, 0xE2, 0x2E, 0x40, 0x9F, 0x96,
                                0xE9, 0x3D, 0x7E, 0x11, 0x73, 0x93, 0x17, 0x2A,
                                0xAE, 0x2D, 0x8A, 0x57, 0x1E, 0x03, 0xAC, 0x9C,
                                0x9E, 0xB7, 0x6F, 0xAC, 0x45, 0xAF, 0x8E, 0x51,
                                0x30, 0xC8, 0x1C, 0x46, 0xA3, 0x5C, 0xE4, 0x11,
                                0xE5, 0xFB, 0xC1, 0x19, 0x1A, 0x0A, 0x52, 0xEF,
                                0xF6, 0x9F, 0x24, 0x45, 0xDF, 0x4F, 0x9B, 0x17,
                                0xAD, 0x2B, 0x41, 0x7B, 0xE6, 0x6C, 0x37, 0x10 };
const uint8_t key[16] = { 0x2B, 0x7E, 0x15, 0x16, 0x28, 0xAE, 0xD2, 0xA6,
                          0xAB, 0xF7, 0x15, 0x88, 0x09, 0xCF, 0x4F, 0x3C };
const uint8_t iv[16] = { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
                         0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F };
uint8_t ciphertext[64]; /* Output buffer for encrypted data (ciphertext). */
AES_CBC128(ciphertext, plaintext, 64, key, iv, true);  /* true means encrypt. */

Typedefs#

typedef void(*

AES_CtrFuncPtr_TypeDef)(uint8_t *ctr)

An AES counter modification function pointer.

Functions#

void

AES_CBC128(uint8_t *out, const uint8_t *in, unsigned int len, const uint8_t *key, const uint8_t *iv, bool encrypt)

Cipher-block chaining (CBC) cipher mode encryption/decryption, 128 bit key.

void

AES_CFB128(uint8_t *out, const uint8_t *in, unsigned int len, const uint8_t *key, const uint8_t *iv, bool encrypt)

Cipher feedback (CFB) cipher mode encryption/decryption, 128 bit key.

void

AES_CTR128(uint8_t *out, const uint8_t *in, unsigned int len, const uint8_t *key, uint8_t *ctr, AES_CtrFuncPtr_TypeDef ctrFunc)

Counter (CTR) cipher mode encryption/decryption, 128 bit key.

void

AES_CTRUpdate32Bit(uint8_t *ctr)

Update last 32 bits of 128 bit counter by incrementing with 1.

void

AES_DecryptKey128(uint8_t *out, const uint8_t *in)

Generate a 128 bit decryption key from the 128 bit encryption key.

void

AES_ECB128(uint8_t *out, const uint8_t *in, unsigned int len, const uint8_t *key, bool encrypt)

Electronic Codebook (ECB) cipher mode encryption/decryption, 128 bit key.

void

AES_OFB128(uint8_t *out, const uint8_t *in, unsigned int len, const uint8_t *key, const uint8_t *iv)

Output feedback (OFB) cipher mode encryption/decryption, 128 bit key.

void

AES_IntClear(uint32_t flags)

Clear one or more pending AES interrupts.

void

AES_IntDisable(uint32_t flags)

Disable one or more AES interrupts.

void

AES_IntEnable(uint32_t flags)

Enable one or more AES interrupts.

uint32_t

AES_IntGet(void)

Get pending AES interrupt flags.

uint32_t

AES_IntGetEnabled(void)

Get enabled and pending AES interrupt flags.

void

AES_IntSet(uint32_t flags)

Set one or more pending AES interrupts from software.

Typedef Documentation#

AES_CtrFuncPtr_TypeDef#

typedef void(* AES_CtrFuncPtr_TypeDef) (uint8_t *ctr) )(uint8_t *ctr)

An AES counter modification function pointer.

Parameters:

ctr - Ptr to byte array (16 bytes) holding a counter to be modified.

Definition at line 110 of file platform/emlib/inc/em_aes.h

Function Documentation#

AES_CBC128#

void AES_CBC128 (uint8_t * out, const uint8_t * in, unsigned int len, const uint8_t * key, const uint8_t * iv, bool encrypt)

Cipher-block chaining (CBC) cipher mode encryption/decryption, 128 bit key.

Parameters

[out]	out	A buffer to place encrypted/decrypted data. Must be at least `len` long. It may be set equal to `in`, in which case the input buffer is overwritten.
[in]	in	A buffer holding data to encrypt/decrypt. Must be at least `len` long.
[in]	len	A number of bytes to encrypt/decrypt. Must be a multiple of 16.
[in]	key	When encrypting, this is the 128 bit encryption key. When decrypting, this is the 128 bit decryption key. The decryption key may be generated from the encryption key with AES_DecryptKey128(). On devices supporting key buffering, this argument can be null. If so, the key will not be loaded as it is assumed the key has been loaded into KEYHA previously.
[in]	iv	128 bit initialization vector.
[in]	encrypt	Set to true to encrypt, false to decrypt.

Encryption:

*           Plaintext                  Plaintext
*               |                          |
*               V                          V
* InitVector ->XOR        +-------------->XOR
*               |         |                |
*               V         |                V
*       +--------------+  |        +--------------+
* Key ->| Block cipher |  |  Key ->| Block cipher |
*       |  encryption  |  |        |  encryption  |
*       +--------------+  |        +--------------+
*               |---------+                |
*               V                          V
*           Ciphertext                 Ciphertext
*

Decryption:

*         Ciphertext                 Ciphertext
*              |----------+                |
*              V          |                V
*       +--------------+  |        +--------------+
* Key ->| Block cipher |  |  Key ->| Block cipher |
*       |  decryption  |  |        |  decryption  |
*       +--------------+  |        +--------------+
*               |         |                |
*               V         |                V
* InitVector ->XOR        +-------------->XOR
*               |                          |
*               V                          V
*           Plaintext                  Plaintext
*

See general comments on layout and byte ordering of parameters.

Definition at line 155 of file platform/emlib/src/em_aes.c

AES_CFB128#

void AES_CFB128 (uint8_t * out, const uint8_t * in, unsigned int len, const uint8_t * key, const uint8_t * iv, bool encrypt)

Cipher feedback (CFB) cipher mode encryption/decryption, 128 bit key.

Parameters

[out]	out	A buffer to place encrypted/decrypted data. Must be at least `len` long. It may be set equal to `in`, in which case the input buffer is overwritten.
[in]	in	A buffer holding data to encrypt/decrypt. Must be at least `len` long.
[in]	len	A number of bytes to encrypt/decrypt. Must be a multiple of 16.
[in]	key	128 bit encryption key is used for both encryption and decryption modes.
[in]	iv	128 bit initialization vector to use.
[in]	encrypt	Set to true to encrypt, false to decrypt.

Encryption:

*           InitVector    +----------------+
*               |         |                |
*               V         |                V
*       +--------------+  |        +--------------+
* Key ->| Block cipher |  |  Key ->| Block cipher |
*       |  encryption  |  |        |  encryption  |
*       +--------------+  |        +--------------+
*               |         |                |
*               V         |                V
*  Plaintext ->XOR        |   Plaintext ->XOR
*               |---------+                |
*               V                          V
*           Ciphertext                 Ciphertext
*

Decryption:

*          InitVector     +----------------+
*               |         |                |
*               V         |                V
*       +--------------+  |        +--------------+
* Key ->| Block cipher |  |  Key ->| Block cipher |
*       |  encryption  |  |        |  encryption  |
*       +--------------+  |        +--------------+
*               |         |                |
*               V         |                V
*              XOR<- Ciphertext           XOR<- Ciphertext
*               |                          |
*               V                          V
*           Plaintext                  Plaintext
*

See general comments on layout and byte ordering of parameters.

Definition at line 440 of file platform/emlib/src/em_aes.c

AES_CTR128#

void AES_CTR128 (uint8_t * out, const uint8_t * in, unsigned int len, const uint8_t * key, uint8_t * ctr, AES_CtrFuncPtr_TypeDef ctrFunc)

Counter (CTR) cipher mode encryption/decryption, 128 bit key.

Parameters

[out]	out	A buffer to place encrypted/decrypted data. Must be at least `len` long. It may be set equal to `in`, in which case the input buffer is overwritten.
[in]	in	A buffer holding data to encrypt/decrypt. Must be at least `len` long.
[in]	len	A number of bytes to encrypt/decrypt. Must be a multiple of 16.
[in]	key	128 bit encryption key. On devices supporting key buffering this argument can be null. If so, the key will not be loaded, as it is assumed the key has been loaded into KEYHA previously.
[inout]	ctr	128 bit initial counter value. The counter is updated after each AES block encoding through use of `ctrFunc`.
[in]	ctrFunc	A function used to update the counter value.

Encryption:

*           Counter                    Counter
*              |                          |
*              V                          V
*       +--------------+           +--------------+
* Key ->| Block cipher |     Key ->| Block cipher |
*       |  encryption  |           |  encryption  |
*       +--------------+           +--------------+
*              |                          |
* Plaintext ->XOR            Plaintext ->XOR
*              |                          |
*              V                          V
*         Ciphertext                 Ciphertext
*

Decryption:

*           Counter                    Counter
*              |                          |
*              V                          V
*       +--------------+           +--------------+
* Key ->| Block cipher |     Key ->| Block cipher |
*       |  encryption  |           |  encryption  |
*       +--------------+           +--------------+
*               |                          |
* Ciphertext ->XOR           Ciphertext ->XOR
*               |                          |
*               V                          V
*           Plaintext                  Plaintext
*

See general comments on layout and byte ordering of parameters.

Definition at line 644 of file platform/emlib/src/em_aes.c

AES_CTRUpdate32Bit#

void AES_CTRUpdate32Bit (uint8_t * ctr)

Update last 32 bits of 128 bit counter by incrementing with 1.

Parameters

[inout]

ctr

A buffer holding 128 bit counter to be updated.

Notice that no special consideration is given to possible wrap around. If 32 least significant bits are 0xFFFFFFFF, they will be updated to 0x00000000, ignoring overflow.

See general comments on layout and byte ordering of parameters.

Definition at line 788 of file platform/emlib/src/em_aes.c

AES_DecryptKey128#

void AES_DecryptKey128 (uint8_t * out, const uint8_t * in)

Generate a 128 bit decryption key from the 128 bit encryption key.

Parameters

[out]	out	A buffer to place 128 bit decryption key. Must be at least 16 bytes long. It may be set equal to `in`, in which case the input buffer is overwritten.
[in]	in	A buffer holding 128 bit encryption key. Must be at least 16 bytes long.

The decryption key is used for some cipher modes when decrypting.

See general comments on layout and byte ordering of parameters.

Definition at line 808 of file platform/emlib/src/em_aes.c

AES_ECB128#

void AES_ECB128 (uint8_t * out, const uint8_t * in, unsigned int len, const uint8_t * key, bool encrypt)

Electronic Codebook (ECB) cipher mode encryption/decryption, 128 bit key.

Parameters

[out]	out	A buffer to place encrypted/decrypted data. Must be at least `len` long. It may be set equal to `in`, in which case the input buffer is overwritten.
[in]	in	A buffer holding data to encrypt/decrypt. Must be at least `len` long.
[in]	len	A number of bytes to encrypt/decrypt. Must be a multiple of 16.
[in]	key	When encrypting, this is the 128 bit encryption key. When decrypting, this is the 128 bit decryption key. The decryption key may be generated from the encryption key with AES_DecryptKey128().
[in]	encrypt	Set to true to encrypt, false to decrypt.

Encryption:

*          Plaintext                  Plaintext
*              |                          |
*              V                          V
*       +--------------+           +--------------+
* Key ->| Block cipher |     Key ->| Block cipher |
*       |  encryption  |           |  encryption  |
*       +--------------+           +--------------+
*              |                          |
*              V                          V
*         Ciphertext                 Ciphertext
*

Decryption:

*         Ciphertext                 Ciphertext
*              |                          |
*              V                          V
*       +--------------+           +--------------+
* Key ->| Block cipher |     Key ->| Block cipher |
*       |  decryption  |           |  decryption  |
*       +--------------+           +--------------+
*              |                          |
*              V                          V
*          Plaintext                  Plaintext
*

See general comments on layout and byte ordering of parameters.

Definition at line 926 of file platform/emlib/src/em_aes.c

AES_OFB128#

void AES_OFB128 (uint8_t * out, const uint8_t * in, unsigned int len, const uint8_t * key, const uint8_t * iv)

Output feedback (OFB) cipher mode encryption/decryption, 128 bit key.

Parameters

[out]	out	A buffer to place encrypted/decrypted data. Must be at least `len` long. It may be set equal to `in`, in which case the input buffer is overwritten.
[in]	in	A buffer holding data to encrypt/decrypt. Must be at least `len` long.
[in]	len	A number of bytes to encrypt/decrypt. Must be a multiple of 16.
[in]	key	128 bit encryption key.
[in]	iv	128 bit initialization vector to use.

Encryption:

*          InitVector    +----------------+
*              |         |                |
*              V         |                V
*       +--------------+ |        +--------------+
* Key ->| Block cipher | |  Key ->| Block cipher |
*       |  encryption  | |        |  encryption  |
*       +--------------+ |        +--------------+
*              |         |                |
*              |---------+                |
*              V                          V
* Plaintext ->XOR            Plaintext ->XOR
*              |                          |
*              V                          V
*         Ciphertext                 Ciphertext
*

Decryption:

*          InitVector    +----------------+
*              |         |                |
*              V         |                V
*       +--------------+ |        +--------------+
* Key ->| Block cipher | |  Key ->| Block cipher |
*       |  encryption  | |        |  encryption  |
*       +--------------+ |        +--------------+
*              |         |                |
*              |---------+                |
*              V                          V
* Ciphertext ->XOR           Ciphertext ->XOR
*              |                          |
*              V                          V
*          Plaintext                  Plaintext
*

See general comments on layout and byte ordering of parameters.

Definition at line 1116 of file platform/emlib/src/em_aes.c

AES_IntClear#

void AES_IntClear (uint32_t flags)

Clear one or more pending AES interrupts.

Parameters

[in]

flags

A pending AES interrupt source to clear. Use a bitwise logic OR combination of valid interrupt flags for the AES module (AES_IF_nnn).

Definition at line 194 of file platform/emlib/inc/em_aes.h

AES_IntDisable#

void AES_IntDisable (uint32_t flags)

Disable one or more AES interrupts.

Parameters

[in]

flags

An AES interrupt sources to disable. Use a bitwise logic OR combination of valid interrupt flags for the AES module (AES_IF_nnn).

Definition at line 207 of file platform/emlib/inc/em_aes.h

AES_IntEnable#

void AES_IntEnable (uint32_t flags)

Enable one or more AES interrupts.

Parameters

[in]

flags

AES interrupt sources to enable. Use a bitwise logic OR combination of valid interrupt flags for the AES module (AES_IF_nnn).

Note

Depending on use, a pending interrupt may already be set prior to enabling the interrupt. Consider using AES_IntClear() prior to enabling if a pending interrupt should be ignored.

Definition at line 225 of file platform/emlib/inc/em_aes.h

AES_IntGet#

uint32_t AES_IntGet (void )

Get pending AES interrupt flags.

Parameters

N/A

Note

This function does not clear event bits.

Returns

AES interrupt sources pending. A bitwise logic OR combination of valid interrupt flags for the AES module (AES_IF_nnn).

Definition at line 241 of file platform/emlib/inc/em_aes.h

AES_IntGetEnabled#

uint32_t AES_IntGetEnabled (void )

Get enabled and pending AES interrupt flags.

Parameters

N/A

Useful for handling more interrupt sources in the same interrupt handler.

Note

This function does not clear interrupt flags.

Returns

Pending and enabled AES interrupt sources. The return value is the bitwise AND of
- the enabled interrupt sources in AES_IEN and
- the pending interrupt flags AES_IF

Definition at line 260 of file platform/emlib/inc/em_aes.h

AES_IntSet#

void AES_IntSet (uint32_t flags)

Set one or more pending AES interrupts from software.

Parameters

[in]

flags

AES interrupt sources to set as pending. Use a bitwise logic OR combination of valid interrupt flags for the AES module (AES_IF_nnn).

Definition at line 276 of file platform/emlib/inc/em_aes.h