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Update getting_started.md

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Guy Wild 2019-09-04 13:45:54 +03:00
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docs/getting_started.md
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@ -191,10 +191,10 @@ Mbed Crypto supports encrypting and decrypting messages using various symmetric
1. Initialize the operation structure to zero or to `PSA_CIPHER_OPERATION_INIT`.
1. Call `psa_cipher_encrypt_setup()` to specify the algorithm and the key to be used.
1. Call either `psa_cipher_generate_iv()` or `psa_cipher_set_iv()` to generate or set the initialization vector (IV). We recommend calling `psa_cipher_generate_iv()`, unless you require a specific IV value.
1. Call `psa_cipher_update()` one or more times, passing the whole message or a fragment of the message on each call.
1. Call `psa_cipher_update()` with the message to encrypt. You may call this function multiple times, passing successive fragments of the message on successive calls.
1. Call `psa_cipher_finish()` to end the operation and output the encrypted message.
This example shows how to encrypt data using an AES (Advanced Encryption Standard) key in CBC (Cipher Block Chaining)) mode with no padding (assuming all prerequisites have been fulfilled):
This example shows how to encrypt data using an AES (Advanced Encryption Standard) key in CBC (Cipher Block Chaining) mode with no padding (assuming all prerequisites have been fulfilled):
```c
enum {
block_size = PSA_BLOCK_CIPHER_BLOCK_SIZE(PSA_KEY_TYPE_AES),
@ -270,9 +270,10 @@ This example shows how to encrypt data using an AES (Advanced Encryption Standar
**To decrypt a message with a symmetric cipher:**
1. Allocate an operation (`psa_cipher_operation_t`) structure to pass to the cipher functions.
1. Call `psa_cipher_decrypt_setup()` to initialize the operation structure and to specify the algorithm and the key to be used.
1. Initialize the operation structure to zero or to `PSA_CIPHER_OPERATION_INIT`.
1. Call `psa_cipher_decrypt_setup()` to specify the algorithm and the key to be used.
1. Call `psa_cipher_set_iv()` with the IV for the decryption.
1. Call `psa_cipher_update()` one or more times, passing the whole message or a fragment of the message on each call.
1. Call `psa_cipher_update()` with the message to encrypt. You may call this function multiple times, passing successive fragments of the message on successive calls.
1. Call `psa_cipher_finish()` to end the operation and output the decrypted message.
This example shows how to decrypt encrypted data using an AES key in CBC mode with no padding
@ -377,10 +378,10 @@ algorithms.
1. Allocate an operation structure (`psa_hash_operation_t`) to pass to the hash functions.
1. Initialize the operation structure to zero or to `PSA_HASH_OPERATION_INIT`.
1. Call `psa_hash_setup()` to specify the hash algorithm.
1. Call `psa_hash_update()` one or more times, passing the whole message or a fragment of the message on each call.
1. Call `psa_hash_update()` with the message to encrypt. You may call this function multiple times, passing successive fragments of the message on successive calls.
1. Call `psa_hash_finish()` to calculate the hash, or `psa_hash_verify()` to compare the computed hash with an expected hash value.
This example shows how to calculate the `SHA-256` hash of a message:
This example shows how to calculate the SHA-256 hash of a message:
```c
psa_status_t status;
psa_algorithm_t alg = PSA_ALG_SHA_256;
@ -425,7 +426,7 @@ This example shows how to calculate the `SHA-256` hash of a message:
mbedtls_psa_crypto_free();
```
This example shows how to verify the `SHA-256` hash of a message:
This example shows how to verify the SHA-256 hash of a message:
```c
psa_status_t status;
psa_algorithm_t alg = PSA_ALG_SHA_256;
@ -477,7 +478,7 @@ The API provides the macro `PSA_HASH_SIZE`, which returns the expected hash leng
#### Handling hash operation contexts
After a successful call to `psa_hash_setup()` initializes the operation structure, you can terminate the operation at any time by calling `psa_hash_abort()`. The call to `psa_hash_abort()` frees any resources associated with the operation, except for the operation structure itself.
After a successful call to `psa_hash_setup()`, you can terminate the operation at any time by calling `psa_hash_abort()`. The call to `psa_hash_abort()` frees any resources associated with the operation, except for the operation structure itself.
Mbed Crypto implicitly calls `psa_hash_abort()` when:
1. A call to `psa_hash_update()` fails (returning any status other than `PSA_SUCCESS`).
@ -545,10 +546,10 @@ information about which inputs to pass when, and when you can obtain which outpu
* Usage flags set for key derivation (`PSA_KEY_USAGE_DERIVE`)
* Key type set to `PSA_KEY_TYPE_DERIVE`.
* Algorithm set to a key derivation algorithm
(for example `PSA_ALG_HKDF(PSA_ALG_SHA_256)`).
(for example, `PSA_ALG_HKDF(PSA_ALG_SHA_256)`).
**To derive a new AES-CTR 128-bit encryption key into a given key slot using HKDF
with a given key, salt and `info`:**
with a given key, salt and info:**
1. Set up the key derivation context using the `psa_key_derivation_setup()`
function, specifying the derivation algorithm `PSA_ALG_HKDF(PSA_ALG_SHA_256)`.
@ -880,6 +881,6 @@ Mbed Crypto provides a simple way to generate a key or key pair.
mbedtls_psa_crypto_free();
```
### More about the Mbed Crypto API
### More about the PSA Crypto API
For more information about the PSA Crypto API, please see the [PSA Cryptography API Specification](https://armmbed.github.io/mbed-crypto/html/index.html).