Mbed Crypto change history

Unreleased changes

In the PSA API, forbid zero-length keys. To pass a zero-length input to a key derivation function, use a buffer instead (this is now always possible).
Rename psa_asymmetric_sign() to psa_sign_hash() and psa_asymmetric_verify() to psa_verify_hash().

The initial seeding of a CTR_DRBG instance makes a second call to the entropy function to obtain entropy for a nonce if the entropy size is less than 3/2 times the key size. In case you want to disable the extra call to grab entropy, you can call mbedtls_ctr_drbg_set_nonce_len() to force the nonce length to 0.

Key derivation inputs in the PSA API can now either come from a key object or from a buffer regardless of the step type.
The CTR_DRBG module can grab a nonce from the entropy source during the initial seeding. The default nonce length is chosen based on the key size to achieve the security strength defined by NIST SP 800-90A. You can change it with mbedtls_ctr_drbg_set_nonce_len().
Add ENUMERATED tag support to the ASN.1 module. Contributed by msopiha-linaro in #307.

Enforce that mbedtls_entropy_func() gathers a total of MBEDTLS_ENTROPY_BLOCK_SIZE bytes or more from strong sources. In the default configuration, on a platform with a single entropy source, the entropy module formerly only grabbed 32 bytes, which is good enough for security if the source is genuinely strong, but less than the expected 64 bytes (size of the entropy accumulator).

Fix a buffer overflow in the PSA HMAC code when using a long key with an unsupported algorithm. Fixes #254.
Fix mbedtls_asn1_get_int to support any number of leading zeros. Credit to OSS-Fuzz for finding a bug in an intermediate version of the fix.
Fix mbedtls_asn1_get_bitstring_null to correctly parse bitstrings of at most 2 bytes.
mbedtls_ctr_drbg_set_entropy_len() and mbedtls_hmac_drbg_set_entropy_len() now work if you call them before mbedtls_ctr_drbg_seed() or mbedtls_hmac_drbg_seed().
Fix some false-positive uninitialized variable warnings. Fix contributed by apple-ihack-geek in ARMmbed/mbedtls#2663.

Remove a useless call to mbedtls_ecp_group_free(). Contributed by Alexander Krizhanovsky in #210.
Speed up PBKDF2 by caching the digest calculation. Contributed by Jack Lloyd and Fortanix Inc in #277.
Small performance improvement of mbedtls_mpi_div_mpi(). Contributed by Alexander Krizhanovsky in #308.

Remove the technical possibility to define custom mbedtls_md_info structures, which was exposed only in an internal header.
psa_close_key(0) and psa_destroy_key(0) now succeed (doing nothing, as before).
Variables containing error codes are now initialized to an error code rather than success, so that coding mistakes or memory corruption tends to cause functions to return this error code rather than a success. There are no known instances where this changes the behavior of the library: this is merely a robustness improvement. #323