diff --git a/include/psa/crypto.h b/include/psa/crypto.h
index 2f972d37d..dcf1ba227 100644
--- a/include/psa/crypto.h
+++ b/include/psa/crypto.h
@@ -698,6 +698,12 @@ typedef uint32_t psa_algorithm_t;
  * This is the ECDSA signature scheme defined by ANSI X9.62,
  * with a random per-message secret number (*k*).
  *
+ * The representation of the signature as a byte string consists of
+ * the concatentation of the signature values *r* and *s*. Each of
+ * *r* and *s* is encoded as an *N*-octet string, where *N* is the length
+ * of the base point of the curve in octets. Each value is represented
+ * in big-endian order (most significant octet first).
+ *
  * \param hash_alg      A hash algorithm (\c PSA_ALG_XXX value such that
  *                      #PSA_ALG_IS_HASH(alg) is true).
  *
@@ -709,7 +715,7 @@ typedef uint32_t psa_algorithm_t;
     (PSA_ALG_ECDSA_BASE | ((hash_alg) & PSA_ALG_HASH_MASK))
 /** ECDSA signature without hashing.
  *
- * This is the signature scheme defined by ANSI X9.62,
+ * This is the same signature scheme as #PSA_ALG_ECDSA(), but
  * without specifying a hash algorithm. This algorithm may only be
  * used to sign or verify a sequence of bytes that should be an
  * already-calculated hash. Note that the input is padded with
@@ -722,6 +728,8 @@ typedef uint32_t psa_algorithm_t;
  *
  * This is the deterministic ECDSA signature scheme defined by RFC 6979.
  *
+ * The representation of a signature is the same as with #PSA_ALG_ECDSA().
+ *
  * Note that when this algorithm is used for verification, signatures
  * made with randomized ECDSA (#PSA_ALG_ECDSA(\c hash_alg)) with the
  * same private key are accepted. In other words,
@@ -1728,34 +1736,15 @@ psa_status_t psa_aead_decrypt( psa_key_slot_t key,
  */
 
 /**
- * \brief Maximum ECDSA signature size for a given curve bit size
+ * \brief ECDSA signature size for a given curve bit size
  *
- * \param curve_bits    Curve size in bits
- * \return              Maximum signature size in bytes
+ * \param curve_bits    Curve size in bits.
+ * \return              Signature size in bytes.
  *
  * \note This macro returns a compile-time constant if its argument is one.
- *
- * \warning This macro may evaluate its argument multiple times.
  */
-/*
- * RFC 4492 page 20:
- *
- *     Ecdsa-Sig-Value ::= SEQUENCE {
- *         r       INTEGER,
- *         s       INTEGER
- *     }
- *
- * Size is at most
- *    1 (tag) + 1 (len) + 1 (initial 0) + curve_bytes for each of r and s,
- *    twice that + 1 (tag) + 2 (len) for the sequence
- * (assuming curve_bytes is less than 126 for r and s,
- * and less than 124 (total len <= 255) for the sequence)
- */
-#define PSA_ECDSA_SIGNATURE_SIZE(curve_bits)                          \
-    ( /*T,L of SEQUENCE*/ ((curve_bits) >= 61 * 8 ? 3 : 2) +          \
-      /*T,L of r,s*/       2 * (((curve_bits) >= 127 * 8 ? 3 : 2) +   \
-      /*V of r,s*/               ((curve_bits) + 8) / 8))
-
+#define PSA_ECDSA_SIGNATURE_SIZE(curve_bits)    \
+    (PSA_BITS_TO_BYTES(curve_bits) * 2)
 
 /** Safe signature buffer size for psa_asymmetric_sign().
  *
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index ffc587a1e..9454f478c 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -40,7 +40,6 @@
 
 #include "mbedtls/arc4.h"
 #include "mbedtls/asn1.h"
-#include "mbedtls/asn1write.h"
 #include "mbedtls/bignum.h"
 #include "mbedtls/blowfish.h"
 #include "mbedtls/camellia.h"
@@ -1640,28 +1639,6 @@ static psa_status_t psa_rsa_decode_md_type( psa_algorithm_t alg,
 }
 
 #if defined(MBEDTLS_ECDSA_C)
-/* Temporary copy from ecdsa.c */
-static int ecdsa_signature_to_asn1( const mbedtls_mpi *r, const mbedtls_mpi *s,
-                                    unsigned char *sig, size_t *slen )
-{
-    int ret;
-    unsigned char buf[MBEDTLS_ECDSA_MAX_LEN];
-    unsigned char *p = buf + sizeof( buf );
-    size_t len = 0;
-
-    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_mpi( &p, buf, s ) );
-    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_mpi( &p, buf, r ) );
-
-    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &p, buf, len ) );
-    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &p, buf,
-                                       MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
-
-    memcpy( sig, p, len );
-    *slen = len;
-
-    return( 0 );
-}
-
 /* `ecp` cannot be const because `ecp->grp` needs to be non-const
  * for mbedtls_ecdsa_sign() and mbedtls_ecdsa_sign_det()
  * (even though these functions don't modify it). */
@@ -1675,11 +1652,16 @@ static psa_status_t psa_ecdsa_sign( mbedtls_ecp_keypair *ecp,
 {
     int ret;
     mbedtls_mpi r, s;
+    size_t curve_bytes = PSA_BITS_TO_BYTES( ecp->grp.pbits );
     mbedtls_mpi_init( &r );
     mbedtls_mpi_init( &s );
 
-    if( signature_size < PSA_ECDSA_SIGNATURE_SIZE( ecp->grp.pbits ) )
-        return( PSA_ERROR_BUFFER_TOO_SMALL );
+    *signature_length = 0;
+    if( signature_size < 2 * curve_bytes )
+    {
+        ret = MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL;
+        goto cleanup;
+    }
 
     if( PSA_ALG_DSA_IS_DETERMINISTIC( alg ) )
     {
@@ -1697,8 +1679,48 @@ static psa_status_t psa_ecdsa_sign( mbedtls_ecp_keypair *ecp,
                                              mbedtls_ctr_drbg_random,
                                              &global_data.ctr_drbg ) );
     }
-    MBEDTLS_MPI_CHK( ecdsa_signature_to_asn1( &r, &s,
-                                              signature, signature_length ) );
+
+    MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &r,
+                                               signature,
+                                               curve_bytes ) );
+    MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &s,
+                                               signature + curve_bytes,
+                                               curve_bytes ) );
+
+cleanup:
+    mbedtls_mpi_free( &r );
+    mbedtls_mpi_free( &s );
+    if( ret == 0 )
+        *signature_length = 2 * curve_bytes;
+    memset( signature + *signature_length, 0,
+            signature_size - *signature_length );
+    return( mbedtls_to_psa_error( ret ) );
+}
+
+static psa_status_t psa_ecdsa_verify( mbedtls_ecp_keypair *ecp,
+                                      const uint8_t *hash,
+                                      size_t hash_length,
+                                      const uint8_t *signature,
+                                      size_t signature_length )
+{
+    int ret;
+    mbedtls_mpi r, s;
+    size_t curve_bytes = PSA_BITS_TO_BYTES( ecp->grp.pbits );
+    mbedtls_mpi_init( &r );
+    mbedtls_mpi_init( &s );
+
+    if( signature_length != 2 * curve_bytes )
+        return( PSA_ERROR_INVALID_SIGNATURE );
+
+    MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &r,
+                                              signature,
+                                              curve_bytes ) );
+    MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &s,
+                                              signature + curve_bytes,
+                                              curve_bytes ) );
+
+    ret = mbedtls_ecdsa_verify( &ecp->grp, hash, hash_length,
+                                &ecp->Q, &r, &s );
 
 cleanup:
     mbedtls_mpi_free( &r );
@@ -1883,13 +1905,9 @@ psa_status_t psa_asymmetric_verify( psa_key_slot_t key,
     {
 #if defined(MBEDTLS_ECDSA_C)
         if( PSA_ALG_IS_ECDSA( alg ) )
-        {
-            int ret;
-            ret = mbedtls_ecdsa_read_signature( slot->data.ecp,
-                                                hash, hash_length,
-                                                signature, signature_length );
-            return( mbedtls_to_psa_error( ret ) );
-        }
+            return( psa_ecdsa_verify( slot->data.ecp,
+                                      hash, hash_length,
+                                      signature, signature_length ) );
         else
 #endif /* defined(MBEDTLS_ECDSA_C) */
         {
diff --git a/tests/suites/test_suite_psa_crypto.data b/tests/suites/test_suite_psa_crypto.data
index 2f9035438..1181fcd92 100644
--- a/tests/suites/test_suite_psa_crypto.data
+++ b/tests/suites/test_suite_psa_crypto.data
@@ -532,7 +532,7 @@ sign_deterministic:PSA_KEY_TYPE_RSA_KEYPAIR:"3082025e02010002818100af057d396ee84
 
 PSA sign: deterministic ECDSA SECP256R1 SHA-256
 depends_on:MBEDTLS_PK_C:MBEDTLS_PK_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_ECDSA_DETERMINISTIC
-sign_deterministic:PSA_KEY_TYPE_ECC_KEYPAIR(PSA_ECC_CURVE_SECP256R1):"3078020101042100ab45435712649cb30bbddac49197eebf2740ffc7f874d9244c3460f54f322d3aa00a06082a8648ce3d030107a14403420004dea5e45d0ea37fc566232a508f4ad20ea13d47e4bf5fa4d54a57a0ba012042087097496efc583fed8b24a5b9be9a51de063f5a00a8b698a16fd7f29b5485f320":PSA_ALG_DETERMINISTIC_ECDSA( PSA_ALG_SHA_256 ):"9ac4335b469bbd791439248504dd0d49c71349a295fee5a1c68507f45a9e1c7b":"304502206a3399f69421ffe1490377adf2ea1f117d81a63cf5bf22e918d51175eb259151022100ce95d7c26cc04e25503e2f7a1ec3573e3c2412534bb4a19b3a7811742f49f50f"
+sign_deterministic:PSA_KEY_TYPE_ECC_KEYPAIR(PSA_ECC_CURVE_SECP256R1):"3078020101042100ab45435712649cb30bbddac49197eebf2740ffc7f874d9244c3460f54f322d3aa00a06082a8648ce3d030107a14403420004dea5e45d0ea37fc566232a508f4ad20ea13d47e4bf5fa4d54a57a0ba012042087097496efc583fed8b24a5b9be9a51de063f5a00a8b698a16fd7f29b5485f320":PSA_ALG_DETERMINISTIC_ECDSA( PSA_ALG_SHA_256 ):"9ac4335b469bbd791439248504dd0d49c71349a295fee5a1c68507f45a9e1c7b":"6a3399f69421ffe1490377adf2ea1f117d81a63cf5bf22e918d51175eb259151ce95d7c26cc04e25503e2f7a1ec3573e3c2412534bb4a19b3a7811742f49f50f"
 
 PSA sign: RSA PKCS#1 v1.5 SHA-256, wrong hash size
 sign_fail:PSA_KEY_TYPE_RSA_KEYPAIR:"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":PSA_ALG_RSA_PKCS1V15_SIGN(PSA_ALG_SHA_256):"ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015":128:PSA_ERROR_INVALID_ARGUMENT
@@ -542,7 +542,7 @@ sign_fail:PSA_KEY_TYPE_RSA_KEYPAIR:"3082025e02010002818100af057d396ee84fb75fdbb5
 
 PSA sign: deterministic ECDSA SECP256R1 SHA-256, output buffer too small
 depends_on:MBEDTLS_PK_C:MBEDTLS_PK_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
-sign_fail:PSA_KEY_TYPE_ECC_KEYPAIR(PSA_ECC_CURVE_SECP256R1):"3078020101042100ab45435712649cb30bbddac49197eebf2740ffc7f874d9244c3460f54f322d3aa00a06082a8648ce3d030107a14403420004dea5e45d0ea37fc566232a508f4ad20ea13d47e4bf5fa4d54a57a0ba012042087097496efc583fed8b24a5b9be9a51de063f5a00a8b698a16fd7f29b5485f320":PSA_ALG_DETERMINISTIC_ECDSA( PSA_ALG_SHA_256 ):"9ac4335b469bbd791439248504dd0d49c71349a295fee5a1c68507f45a9e1c7b":10:PSA_ERROR_BUFFER_TOO_SMALL
+sign_fail:PSA_KEY_TYPE_ECC_KEYPAIR(PSA_ECC_CURVE_SECP256R1):"3078020101042100ab45435712649cb30bbddac49197eebf2740ffc7f874d9244c3460f54f322d3aa00a06082a8648ce3d030107a14403420004dea5e45d0ea37fc566232a508f4ad20ea13d47e4bf5fa4d54a57a0ba012042087097496efc583fed8b24a5b9be9a51de063f5a00a8b698a16fd7f29b5485f320":PSA_ALG_DETERMINISTIC_ECDSA( PSA_ALG_SHA_256 ):"9ac4335b469bbd791439248504dd0d49c71349a295fee5a1c68507f45a9e1c7b":63:PSA_ERROR_BUFFER_TOO_SMALL
 
 PSA sign: deterministic ECDSA SECP256R1, invalid hash
 depends_on:MBEDTLS_PK_C:MBEDTLS_PK_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_ECDSA_DETERMINISTIC
@@ -562,11 +562,15 @@ asymmetric_verify_fail:PSA_KEY_TYPE_RSA_KEYPAIR:"3082025e02010002818100af057d396
 
 PSA verify: ECDSA SECP256R1, good
 depends_on:MBEDTLS_PK_C:MBEDTLS_PK_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
-asymmetric_verify:PSA_KEY_TYPE_ECC_KEYPAIR(PSA_ECC_CURVE_SECP256R1):"3078020101042100ab45435712649cb30bbddac49197eebf2740ffc7f874d9244c3460f54f322d3aa00a06082a8648ce3d030107a14403420004dea5e45d0ea37fc566232a508f4ad20ea13d47e4bf5fa4d54a57a0ba012042087097496efc583fed8b24a5b9be9a51de063f5a00a8b698a16fd7f29b5485f320":PSA_ALG_ECDSA_ANY:"9ac4335b469bbd791439248504dd0d49c71349a295fee5a1c68507f45a9e1c7b":"304502206a3399f69421ffe1490377adf2ea1f117d81a63cf5bf22e918d51175eb259151022100ce95d7c26cc04e25503e2f7a1ec3573e3c2412534bb4a19b3a7811742f49f50f"
+asymmetric_verify:PSA_KEY_TYPE_ECC_KEYPAIR(PSA_ECC_CURVE_SECP256R1):"3078020101042100ab45435712649cb30bbddac49197eebf2740ffc7f874d9244c3460f54f322d3aa00a06082a8648ce3d030107a14403420004dea5e45d0ea37fc566232a508f4ad20ea13d47e4bf5fa4d54a57a0ba012042087097496efc583fed8b24a5b9be9a51de063f5a00a8b698a16fd7f29b5485f320":PSA_ALG_ECDSA_ANY:"9ac4335b469bbd791439248504dd0d49c71349a295fee5a1c68507f45a9e1c7b":"6a3399f69421ffe1490377adf2ea1f117d81a63cf5bf22e918d51175eb259151ce95d7c26cc04e25503e2f7a1ec3573e3c2412534bb4a19b3a7811742f49f50f"
 
-PSA verify: ECDSA SECP256R1, wrong signature
+PSA verify: ECDSA SECP256R1, wrong signature size (correct but ASN1-encoded)
 depends_on:MBEDTLS_PK_C:MBEDTLS_PK_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
-asymmetric_verify_fail:PSA_KEY_TYPE_ECC_KEYPAIR(PSA_ECC_CURVE_SECP256R1):"3078020101042100ab45435712649cb30bbddac49197eebf2740ffc7f874d9244c3460f54f322d3aa00a06082a8648ce3d030107a14403420004dea5e45d0ea37fc566232a508f4ad20ea13d47e4bf5fa4d54a57a0ba012042087097496efc583fed8b24a5b9be9a51de063f5a00a8b698a16fd7f29b5485f320":PSA_ALG_ECDSA_ANY:"9ac4335b469bbd791439248504dd0d49c71349a295fee5a1c68507f45a9e1c7b":"304502206a3399f69421ffe1490377adf2ea1f117d81a63cf5bf22e918d51175eb259151022100ce95d7c26cc04e25503e2f7a1ec3573e3c2412534bb4a19b3a7811742f49f50e":PSA_ERROR_INVALID_SIGNATURE
+asymmetric_verify_fail:PSA_KEY_TYPE_ECC_KEYPAIR(PSA_ECC_CURVE_SECP256R1):"3078020101042100ab45435712649cb30bbddac49197eebf2740ffc7f874d9244c3460f54f322d3aa00a06082a8648ce3d030107a14403420004dea5e45d0ea37fc566232a508f4ad20ea13d47e4bf5fa4d54a57a0ba012042087097496efc583fed8b24a5b9be9a51de063f5a00a8b698a16fd7f29b5485f320":PSA_ALG_ECDSA_ANY:"9ac4335b469bbd791439248504dd0d49c71349a295fee5a1c68507f45a9e1c7b":"304502206a3399f69421ffe1490377adf2ea1f117d81a63cf5bf22e918d51175eb259151022100ce95d7c26cc04e25503e2f7a1ec3573e3c2412534bb4a19b3a7811742f49f50f":PSA_ERROR_INVALID_SIGNATURE
+
+PSA verify: ECDSA SECP256R1, wrong signature of correct size
+depends_on:MBEDTLS_PK_C:MBEDTLS_PK_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+asymmetric_verify_fail:PSA_KEY_TYPE_ECC_KEYPAIR(PSA_ECC_CURVE_SECP256R1):"3078020101042100ab45435712649cb30bbddac49197eebf2740ffc7f874d9244c3460f54f322d3aa00a06082a8648ce3d030107a14403420004dea5e45d0ea37fc566232a508f4ad20ea13d47e4bf5fa4d54a57a0ba012042087097496efc583fed8b24a5b9be9a51de063f5a00a8b698a16fd7f29b5485f320":PSA_ALG_ECDSA_ANY:"9ac4335b469bbd791439248504dd0d49c71349a295fee5a1c68507f45a9e1c7b":"6a3399f69421ffe1490377adf2ea1f117d81a63cf5bf22e918d51175eb259151ce95d7c26cc04e25503e2f7a1ec3573e3c2412534bb4a19b3a7811742f49f50e":PSA_ERROR_INVALID_SIGNATURE
 
 PSA encrypt-decrypt: RSA PKCS#1 v1.5 vector #1
 depends_on:MBEDTLS_PK_PARSE_C:MBEDTLS_RSA_C:MBEDTLS_PKCS1_V15