openssl: Encoding of EC Public keys is broken

Using the new Encoder APIs to encode EC public keys seems to be broken.

Here is a reproducer:

#include <openssl/encoder.h>
#include <openssl/evp.h>
#include <openssl/ec.h>
#include <string.h>
#include <openssl/bio.h>

int main(void) {
    EVP_PKEY *key = EVP_EC_gen("P-256");
    unsigned char *publicKey = NULL;
    size_t publicLen = 0;
    BIO *out;
    OSSL_ENCODER_CTX *ctx
        = OSSL_ENCODER_CTX_new_for_pkey(key, EVP_PKEY_PUBLIC_KEY, "DER", NULL,
                                        NULL);
    if (ctx == NULL)
        abort();
    if (!OSSL_ENCODER_to_data(ctx, &publicKey, &publicLen))
        abort();
    OSSL_ENCODER_CTX_free(ctx);

    BIO_dump_fp(stdout, publicKey, publicLen);
    out = BIO_new_file("ecpubkey.der", "wb");
    BIO_write(out, publicKey, publicLen);

    printf("Success\n");

    return 0;
}

Running this gives output like this:

0000 - 04 da 56 4c 0c 45 48 88-eb 4b ee a6 2a c1 47 61   ..VL.EH..K..*.Ga
0010 - f5 f9 9d 84 4e a2 42 59-0d c6 77 94 e2 2b 5a 8c   ....N.BY..w..+Z.
0020 - 31 8a 42 fc 4a a2 76 5c-99 64 5d 5b bb c5 00 8c   1.B.J.v\.d][....
0030 - fb 94 f0 06 7a d3 dc 1e-06 76 46 d7 00 d1 42 09   ....z....vF...B.
0040 - 08                                                .
Success

With the output in a file “ecpubkey.der”. Trying to use that output file fails:

$ openssl ec -in ecpubkey.der -pubin -inform DER
read EC key
Could not read public key from ecpubkey.der
unable to load Key

Inspecting the DER is also interesting:

$ openssl asn1parse -in ecpubkey.der -inform DER
Error in encoding
4007080A647F0000:error:0680007B:asn1 encoding routines:ASN1_get_object:header too long:crypto/asn1/asn1_lib.c:105:

Modifying the above reproducer to change the string “DER” to “PEM”, gives out an output file like this:

-----BEGIN EC PUBLIC KEY-----
BMzAylbS4lDBJFEMSMf6ZnnBqcHyP6ERRK1jwlJ6/3he0XP0QDPyOb981WxU3BcZ
4/m9TUWdk7TN/P8d6o8khak=
-----END EC PUBLIC KEY-----

Which has a PEM header of “EC PUBLIC KEY” so this means it contains a …wait…what??? Is there such a thing as an “EC PUBLIC KEY” file??? Don’t we just use SPKI format for EC public keys???