diff --git a/library/rsa.c b/library/rsa.c
index d879a30..5e7cbcc 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -54,6 +54,18 @@
 #include <stdlib.h>
 #endif
 
+/* We use MD first if it's available (for compatibility reasons)
+ * and "fall back" to PSA otherwise (which needs psa_crypto_init()). */
+#if defined(MBEDTLS_PKCS1_V21)
+#if defined(MBEDTLS_MD_C)
+#define HASH_MAX_SIZE   MBEDTLS_MD_MAX_SIZE
+#else /* MBEDTLS_MD_C */
+#include "psa/crypto.h"
+#include "mbedtls/psa_util.h"
+#define HASH_MAX_SIZE   PSA_HASH_MAX_SIZE
+#endif /* MBEDTLS_MD_C */
+#endif /* MBEDTLS_PKCS1_V21 */
+
 #if defined(MBEDTLS_PLATFORM_C)
 #include "mbedtls/platform.h"
 #else
@@ -1086,6 +1098,25 @@
 }
 
 #if defined(MBEDTLS_PKCS1_V21)
+#if !defined(MBEDTLS_MD_C)
+static int ret_from_status( psa_status_t status )
+{
+    switch( status )
+    {
+        case PSA_SUCCESS:
+            return( 0 );
+        case PSA_ERROR_NOT_SUPPORTED:
+            return( MBEDTLS_ERR_MD_FEATURE_UNAVAILABLE );
+        case PSA_ERROR_INVALID_ARGUMENT:
+            return( MBEDTLS_ERR_MD_BAD_INPUT_DATA );
+        case PSA_ERROR_INSUFFICIENT_MEMORY:
+            return( MBEDTLS_ERR_MD_ALLOC_FAILED );
+        default:
+            return( MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED );
+    }
+}
+#endif /* !MBEDTLS_MD_C */
+
 /**
  * Generate and apply the MGF1 operation (from PKCS#1 v2.1) to a buffer.
  *
@@ -1098,19 +1129,17 @@
 static int mgf_mask( unsigned char *dst, size_t dlen, unsigned char *src,
                       size_t slen, mbedtls_md_type_t md_alg )
 {
-    const mbedtls_md_info_t *md_info;
-    mbedtls_md_context_t md_ctx;
-    unsigned char mask[MBEDTLS_MD_MAX_SIZE];
     unsigned char counter[4];
     unsigned char *p;
     unsigned int hlen;
     size_t i, use_len;
+    unsigned char mask[HASH_MAX_SIZE];
+#if defined(MBEDTLS_MD_C)
     int ret = 0;
+    const mbedtls_md_info_t *md_info;
+    mbedtls_md_context_t md_ctx;
 
     mbedtls_md_init( &md_ctx );
-    memset( mask, 0, MBEDTLS_MD_MAX_SIZE );
-    memset( counter, 0, 4 );
-
     md_info = mbedtls_md_info_from_type( md_alg );
     if( md_info == NULL )
         return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
@@ -1120,6 +1149,17 @@
         goto exit;
 
     hlen = mbedtls_md_get_size( md_info );
+#else
+    psa_hash_operation_t op = PSA_HASH_OPERATION_INIT;
+    psa_algorithm_t alg = mbedtls_psa_translate_md( md_alg );
+    psa_status_t status = PSA_SUCCESS;
+    size_t out_len;
+
+    hlen = PSA_HASH_LENGTH( alg );
+#endif
+
+    memset( mask, 0, sizeof( mask ) );
+    memset( counter, 0, 4 );
 
     /* Generate and apply dbMask */
     p = dst;
@@ -1130,6 +1170,7 @@
         if( dlen < hlen )
             use_len = dlen;
 
+#if defined(MBEDTLS_MD_C)
         if( ( ret = mbedtls_md_starts( &md_ctx ) ) != 0 )
             goto exit;
         if( ( ret = mbedtls_md_update( &md_ctx, src, slen ) ) != 0 )
@@ -1138,6 +1179,17 @@
             goto exit;
         if( ( ret = mbedtls_md_finish( &md_ctx, mask ) ) != 0 )
             goto exit;
+#else
+        if( ( status = psa_hash_setup( &op, alg ) ) != PSA_SUCCESS )
+            goto exit;
+        if( ( status = psa_hash_update( &op, src, slen ) ) != PSA_SUCCESS )
+            goto exit;
+        if( ( status = psa_hash_update( &op, counter, 4 ) ) != PSA_SUCCESS )
+            goto exit;
+        status = psa_hash_finish( &op, mask, sizeof( mask ), &out_len );
+        if( status != PSA_SUCCESS )
+            goto exit;
+#endif
 
         for( i = 0; i < use_len; ++i )
             *p++ ^= mask[i];
@@ -1148,10 +1200,16 @@
     }
 
 exit:
-    mbedtls_md_free( &md_ctx );
     mbedtls_platform_zeroize( mask, sizeof( mask ) );
+#if defined(MBEDTLS_MD_C)
+    mbedtls_md_free( &md_ctx );
 
     return( ret );
+#else
+    psa_hash_abort( &op );
+
+    return( ret_from_status( status ) );
+#endif
 }
 
 /**
@@ -1169,6 +1227,8 @@
                         unsigned char *out, mbedtls_md_type_t md_alg )
 {
     const unsigned char zeros[8] = { 0, 0, 0, 0, 0, 0, 0, 0 };
+
+#if defined(MBEDTLS_MD_C)
     mbedtls_md_context_t md_ctx;
     int ret;
 
@@ -1194,6 +1254,30 @@
     mbedtls_md_free( &md_ctx );
 
     return( ret );
+#else
+    psa_hash_operation_t op = PSA_HASH_OPERATION_INIT;
+    psa_algorithm_t alg = mbedtls_psa_translate_md( md_alg );
+    psa_status_t status = PSA_SUCCESS;
+    size_t out_size = PSA_HASH_LENGTH( alg );
+    size_t out_len;
+
+    if( ( status = psa_hash_setup( &op, alg ) ) != PSA_SUCCESS )
+        goto exit;
+    if( ( status = psa_hash_update( &op, zeros, sizeof( zeros ) ) ) != PSA_SUCCESS )
+        goto exit;
+    if( ( status = psa_hash_update( &op, hash, hlen ) ) != PSA_SUCCESS )
+        goto exit;
+    if( ( status = psa_hash_update( &op, salt, slen ) ) != PSA_SUCCESS )
+        goto exit;
+    status = psa_hash_finish( &op, out, out_size, &out_len );
+    if( status != PSA_SUCCESS )
+        goto exit;
+
+exit:
+    psa_hash_abort( &op );
+
+    return( ret_from_status( status ) );
+#endif /* !MBEDTLS_MD_C */
 }
 
 /**
@@ -1208,6 +1292,7 @@
                          const unsigned char *input, size_t ilen,
                          unsigned char *output )
 {
+#if defined(MBEDTLS_MD_C)
     const mbedtls_md_info_t *md_info;
 
     md_info = mbedtls_md_info_from_type( md_alg );
@@ -1215,6 +1300,16 @@
         return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
 
     return( mbedtls_md( md_info, input, ilen, output ) );
+#else
+    psa_algorithm_t alg = mbedtls_psa_translate_md( md_alg );
+    psa_status_t status;
+    size_t out_size = PSA_HASH_LENGTH( alg );
+    size_t out_len;
+
+    status = psa_hash_compute( alg, input, ilen, output, out_size, &out_len );
+
+    return( ret_from_status( status ) );
+#endif /* !MBEDTLS_MD_C */
 }
 #endif /* MBEDTLS_PKCS1_V21 */
 
@@ -1393,7 +1488,7 @@
     size_t ilen, i, pad_len;
     unsigned char *p, bad, pad_done;
     unsigned char buf[MBEDTLS_MPI_MAX_SIZE];
-    unsigned char lhash[MBEDTLS_MD_MAX_SIZE];
+    unsigned char lhash[HASH_MAX_SIZE];
     unsigned int hlen;
 
     RSA_VALIDATE_RET( ctx != NULL );
@@ -1988,7 +2083,7 @@
     size_t siglen;
     unsigned char *p;
     unsigned char *hash_start;
-    unsigned char result[MBEDTLS_MD_MAX_SIZE];
+    unsigned char result[HASH_MAX_SIZE];
     unsigned int hlen;
     size_t observed_salt_len, msb;
     unsigned char buf[MBEDTLS_MPI_MAX_SIZE] = {0};