AES - AES Accelerator

Description

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:

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. */

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_CBC256 (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, 256 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_CFB256 (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, 256 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_CTR256 (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, 256 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_DecryptKey256 (uint8_t *out, const uint8_t *in)
Generate a 256 bit decryption key from the 256 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_ECB256 (uint8_t *out, const uint8_t *in, unsigned int len, const uint8_t *key, bool encrypt)
Electronic Codebook (ECB) cipher mode encryption/decryption, 256 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_OFB256 (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, 256 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.

Typedefs

typedef void(* AES_CtrFuncPtr_TypeDef ) (uint8_t *ctr)
An AES counter modification function pointer.

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.

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.

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.

◆ AES_CBC256()

void AES_CBC256 ( 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, 256 bit key.

See AES_CBC128() for the CBC figure.

See general comments on layout and byte ordering of parameters.

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 256 bit encryption key. When decrypting, this is the 256 bit decryption key. The decryption key may be generated from the encryption key with AES_DecryptKey256() .
[in] iv 128 bit initialization vector to use.
[in] encrypt Set to true to encrypt, false to decrypt.

◆ 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.

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.

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.

◆ AES_CFB256()

void AES_CFB256 ( 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, 256 bit key.

See AES_CFB128() for the CFB figure.

See general comments on layout and byte ordering of parameters.

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 256 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.

◆ 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.

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.

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.
[in,out] 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.

◆ AES_CTR256()

void AES_CTR256 ( 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, 256 bit key.

See AES_CTR128() for CTR figure.

See general comments on layout and byte ordering of parameters.

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 256 bit encryption key.
[in,out] ctr 128 bit initial counter value. The counter is updated after each AES block encoding through use of ctrFunc .
[in] ctrFunc Function used to update counter value.

◆ AES_CTRUpdate32Bit()

void AES_CTRUpdate32Bit ( uint8_t * ctr )

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

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.

Parameters
[in,out] ctr A buffer holding 128 bit counter to be updated.

◆ AES_DecryptKey128()

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

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

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

See general comments on layout and byte ordering of parameters.

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.

◆ AES_DecryptKey256()

void AES_DecryptKey256 ( uint8_t * out,
const uint8_t * in
)

Generate a 256 bit decryption key from the 256 bit encryption key.

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

See general comments on layout and byte ordering of parameters.

Parameters
[out] out A buffer to place 256 bit decryption key. Must be at least 32 bytes long. It may be set equal to in , in which case the input buffer is overwritten.
[in] in A buffer holding 256 bit encryption key. Must be at least 32 bytes long.

◆ 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.

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.

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.

◆ AES_ECB256()

void AES_ECB256 ( uint8_t * out,
const uint8_t * in,
unsigned int len,
const uint8_t * key,
bool encrypt
)

Electronic Codebook (ECB) cipher mode encryption/decryption, 256 bit key.

See AES_ECB128() for the ECB figure.

See general comments on layout and byte ordering of parameters.

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 256 bit encryption key. When decrypting, this is the 256 bit decryption key. The decryption key may be generated from the encryption key with AES_DecryptKey256() .
[in] encrypt Set to true to encrypt, false to decrypt.

◆ 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.

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.

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.

◆ AES_OFB256()

void AES_OFB256 ( 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, 256 bit key.

See AES_OFB128() for OFB figure.

See general comments on layout and byte ordering of parameters.

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 256 bit encryption key.
[in] iv 128 bit initialization vector to use.

◆ AES_IntClear()

void AES_IntClear ( uint32_t flags )
inline

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).

◆ AES_IntDisable()

void AES_IntDisable ( uint32_t flags )
inline

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).

◆ AES_IntEnable()

void AES_IntEnable ( uint32_t flags )
inline

Enable one or more AES interrupts.

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.
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).

◆ AES_IntGet()

uint32_t AES_IntGet ( void )
inline

Get pending AES interrupt flags.

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).

◆ AES_IntGetEnabled()

uint32_t AES_IntGetEnabled ( void )
inline

Get enabled and pending AES interrupt flags.

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

◆ AES_IntSet()

void AES_IntSet ( uint32_t flags )
inline

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).

Typedef Documentation

◆ AES_CtrFuncPtr_TypeDef

typedef void(* AES_CtrFuncPtr_TypeDef) (uint8_t *ctr)

An AES counter modification function pointer.

Parameters:

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