20 May
2026
20 May
'26
8:40 p.m.
Hello,
The error seems to be a key policy check returning -133 (PSA_ERROR_NOT_PERMITTED). I notice your code specifies PSA_ALG_HKDF(PSA_ALG_SHA_256) as the algorithm in the key policy, and PSA_ALG_SHA_256 when calling psa_sign_hash(). The two need to match, and neither of these two is a signature algorithm. You presumably meant PSA_ALG_RSA_PKCS1V15_SIGN(PSA_ALG_SHA_256) in both cases. (In the attributes, the other plausible algorithm is PSA_ALG_RSA_PKCS1V15_SIGN(PSA_ALG_ANY_HASH), if you want the key to be usable with different hash algorithms.)
--
Best regards,
Gilles Peskine
TF-PSA-Crypto developer
On 20/05/2026 20:13, Danny Backx via mbed-tls wrote:
>
> I got into trouble with migrating to the latest (v6.0) version of
> esp-idf, because it implies a migration to mbedtls 4.0.
>
> I had a working application (library really) to obtain ACME
> certificates from letsencrypt.org. I tried porting, but ran into
> trouble. So please help.
>
> To debug, I try to mimic the example in Appendix A.2 of RFC 7515.
> Where this should obviously succeed, the current output I get is :
>
> I (12:57:46.067) main_task: Calling app_main()
> I (12:57:46.088) Crypto: Acme standalone client example © 2026 by
> Danny Backx
> I (12:57:46.089) Crypto: checkRfc7515_a21 Base64({"alg":"RS256"}) ->
> eyJhbGciOiJSUzI1NiJ9 is correct
> I (12:57:46.094) Crypto: checkRfc7515_a21 Base64({"iss":"joe",
> "exp":1300819380,
> "http://example.com/is_root%22:true%7D) ->
> eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ
> is correct
> I (12:57:46.121) Crypto: checkRfc7515_a21 importPrivateKey() -> 1073741825
> E (12:57:46.122) psa_crypto: psa_get_and_lock_key_slot_with_policy
> psa_key_policy_permits -> -133
> E (12:57:46.129) psa_crypto: psa_sign_internal
> psa_get_and_lock_key_slot_with_policy -> -133
> E (12:57:46.137) Crypto: psa_sign_hash (key 1073741825) failed (not
> permitted, -133 0x0085)
> I (12:57:46.145) Crypto: checkRfc7515_a21
> Signature(eyJhbGciOiJSUzI1NiJ9,eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ)
> -> (null)
> E (12:57:46.161) Crypto: Signature 0, fail
> E (12:57:46.165) Crypto: RFC 7515 A.2.1 : validation failed
>
> Some of the "psa_crypto" lines come from debug statements I added in
> the library.
>
> The whole source for this is in one file at
> https://sourceforge.net/p/esp32-acme-client/code/HEAD/tree/trunk/examples/si...
> . Obviously it's the hashing step which I had under control with a
> previous library which I don't call correctly (or I don't know how to
> import the right key).
>
> What am I doing wrong ?
>
> Thanks,
>
> Danny
>
> --
> Danny Backx - dannybackx@telenet.be
>