Remove PKCSv1.5 sig format option from RSA

Since we are changing the image header format, there is no reason to
continue to support the old PKCS#1 v1.5 signatures.  Remove the
definitions, and conditional complication related to this, and only
support the newer PSS signatures.

Signed-off-by: Marko Kiiskila <marko@runtime.io>
Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/Makefile b/Makefile
index 533aff2..ca6b4ce 100644
--- a/Makefile
+++ b/Makefile
@@ -12,10 +12,6 @@
 CONF_FILE = boot/zephyr/prj.conf
 CFLAGS += -DMCUBOOT_SIGN_RSA -DMCUBOOT_USE_MBED_TLS
 
-# Newer uses should use the RSA-PSS signature algorithm.  This define
-# enables (and requires) this type of signature.
-#CFLAGS += -DMCUBOOT_RSA_PKCS1_15
-
 # ECDSA P-256
 #CONF_FILE = boot/zephyr/prj-p256.conf
 #CFLAGS += -DMCUBOOT_SIGN_EC256 -DMCUBOOT_USE_TINYCRYPT
diff --git a/boot/bootutil/src/image_rsa.c b/boot/bootutil/src/image_rsa.c
index d452064..88ec784 100644
--- a/boot/bootutil/src/image_rsa.c
+++ b/boot/bootutil/src/image_rsa.c
@@ -32,15 +32,6 @@
 
 #include "bootutil_priv.h"
 
-#ifdef  MCUBOOT_RSA_PKCS1_15
-static const uint8_t sha256_oid[] = {
-    0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86,
-    0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05,
-    0x00, 0x04, 0x20
-};
-#endif
-
-#ifndef MCUBOOT_RSA_PKCS1_15
 /*
  * Constants for this particular constrained implementation of
  * RSA-PSS.  In particular, we support RSA 2048, with a SHA256 hash,
@@ -70,7 +61,6 @@
 #define PSS_MASK_SALT_POS   (PSS_MASK_ONE_POS + 1)
 
 static const uint8_t pss_zeros[8] = {0};
-#endif
 
 /*
  * Parse the public key used for signing. Simple RSA format.
@@ -108,7 +98,6 @@
     return 0;
 }
 
-#ifndef MCUBOOT_RSA_PKCS1_15
 /*
  * Compute the RSA-PSS mask-generation function, MGF1.  Assumptions
  * are that the mask length will be less than 256 * PSS_HLEN, and
@@ -263,55 +252,6 @@
 
     return 0;
 }
-#else /* MCUBOOT_RSA_PKCS1_15 */
-/*
- * PKCS1.5 using RSA2048 computed over SHA256.
- */
-static int
-bootutil_cmp_rsasig(mbedtls_rsa_context *ctx, uint8_t *hash, uint32_t hlen,
-  uint8_t *sig)
-{
-    uint8_t buf[MBEDTLS_MPI_MAX_SIZE];
-    uint8_t *p;
-
-    if (ctx->len != 256) {
-        return -1;
-    }
-
-    if (mbedtls_rsa_public(ctx, sig, buf)) {
-        return -1;
-    }
-
-    p = buf;
-
-    if (*p++ != 0 || *p++ != MBEDTLS_RSA_SIGN) {
-        return -1;
-    }
-
-    while (*p != 0) {
-        if (p >= buf + ctx->len - 1 || *p != 0xFF) {
-            return -1;
-        }
-        p++;
-    }
-    p++;
-
-    if ((p - buf) + sizeof(sha256_oid) + hlen != ctx->len) {
-        return -1;
-    }
-
-    if (memcmp(p, sha256_oid, sizeof(sha256_oid))) {
-        return -1;
-    }
-    p += sizeof(sha256_oid);
-
-    if (memcmp(p, hash, hlen)) {
-        return -1;
-    }
-
-    return 0;
-}
-#endif
 
 int
 bootutil_verify_sig(uint8_t *hash, uint32_t hlen, uint8_t *sig, int slen,
diff --git a/boot/mynewt/mcuboot_config/include/mcuboot_config/mcuboot_config.h b/boot/mynewt/mcuboot_config/include/mcuboot_config/mcuboot_config.h
index 416bf9e..fcc2fc5 100644
--- a/boot/mynewt/mcuboot_config/include/mcuboot_config/mcuboot_config.h
+++ b/boot/mynewt/mcuboot_config/include/mcuboot_config/mcuboot_config.h
@@ -33,9 +33,6 @@
 #if MYNEWT_VAL(BOOTUTIL_SIGN_RSA)
 #define MCUBOOT_SIGN_RSA 1
 #endif
-#if MYNEWT_VAL(BOOTUTIL_RSA_PKCS1_15)
-#define MCUBOOT_RSA_PKCS1_15 1
-#endif
 #if MYNEWT_VAL(BOOTUTIL_SIGN_EC)
 #define MCUBOOT_SIGN_EC 1
 #endif
diff --git a/boot/mynewt/mcuboot_config/syscfg.yml b/boot/mynewt/mcuboot_config/syscfg.yml
index 574aa37..7e8d241 100644
--- a/boot/mynewt/mcuboot_config/syscfg.yml
+++ b/boot/mynewt/mcuboot_config/syscfg.yml
@@ -25,9 +25,6 @@
     BOOTUTIL_SIGN_RSA:
         description: 'Images are signed using RSA2048.'
         value: 0
-    BOOTUTIL_RSA_PKCS1_15:
-        description: 'Sign using old PKCS#1 1.5 (otherwise uses PSS)'
-        value: 0
     BOOTUTIL_SIGN_EC:
         description: 'Images are signed using ECDSA NIST P-224.'
         value: 0