| ## Compile-time configuration |
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| ### Configuration file split |
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| All configuration options that are relevant to TF-PSA-Crypto must now be configured in one of its configuration files, namely: |
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| * `TF_PSA_CRYPTO_CONFIG_FILE`, if set on the preprocessor command line; |
| * otherwise `<psa/crypto_config.h>`; |
| * additionally `TF_PSA_CRYPTO_USER_CONFIG_FILE`, if set. |
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| Configuration options that are relevant to X.509 or TLS should still be set in the Mbed TLS configuration file (`MBEDTLS_CONFIG_FILE` or `<mbedtls/mbedtls_config.h>`, plus `MBEDTLS_USER_CONFIG_FILE` if it is set). However, you can define all options in the crypto configuration, and Mbed TLS will pick them up. |
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| Generally speaking, the options that must be configured in TF-PSA-Crypto are: |
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| * options related to platform settings; |
| * options related to the choice of cryptographic mechanisms included in the build; |
| * options related to the inner workings of cryptographic mechanisms, such as size/memory/performance compromises; |
| * options related to crypto-adjacent features, such as ASN.1 and Base64. |
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| See `include/psa/crypto_config.h` in TF-PSA-Crypto and `include/mbedtls/mbedtls_config.h` in Mbed TLS for details. |
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| Notably, `<psa/crypto_config.h>` is no longer limited to `PSA_WANT_xxx` options. |
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| Note that many options related to cryptography have changed; see the TF-PSA-Crypto migration guide for details. |
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| ### Split of `build_info.h` and `version.h` |
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| The header file `<mbedtls/build_info.h>`, which includes the configuration file and provides the adjusted configuration macros, now has an similar file `<tf-psa-crypto/build_info.h>` in TF-PSA-Crypto. The Mbed TLS header includes the TF-PSA-Crypto header, so including `<mbedtls/build_info.h>` remains sufficient to obtain information about the crypto configuration. |
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| TF-PSA-Crypto exposes its version through `<tf-psa-crypto/version.h>`, similar to `<mbedtls/version.h>` in Mbed TLS. |
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| ### Removal of `check_config.h` |
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| The header `mbedtls/check_config.h` is no longer present. Including it from user configuration files was already obsolete in Mbed TLS 3.x, since it enforces properties the configuration as adjusted by `mbedtls/build_info.h`, not properties that the user configuration is expected to meet. |
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| ### Changes to TLS options |
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| #### Enabling null cipher suites |
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| The option to enable null cipher suites in TLS 1.2 has been renamed from `MBEDTLS_CIPHER_NULL_CIPHER` to `MBEDTLS_SSL_NULL_CIPHERSUITES`. It remains disabled in the default configuration. |
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| #### Removal of backward compatibility options |
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| The option `MBEDTLS_SSL_DTLS_CONNECTION_ID_COMPAT` has been removed. Only the version standardized in RFC 9146 is supported now. |