homed: move helper calls for RSA encryption to shared code

src/shared/openssl-util.c

@@ -0,0 +1,41 @@
+#include "openssl-util.h"
+#include "alloc-util.h"
+
+#if HAVE_OPENSSL
+int rsa_encrypt_bytes(
+                EVP_PKEY *pkey,
+                const void *decrypted_key,
+                size_t decrypted_key_size,
+                void **ret_encrypt_key,
+                size_t *ret_encrypt_key_size) {
+
+        _cleanup_(EVP_PKEY_CTX_freep) EVP_PKEY_CTX *ctx = NULL;
+        _cleanup_free_ void *b = NULL;
+        size_t l;
+
+        ctx = EVP_PKEY_CTX_new(pkey, NULL);
+        if (!ctx)
+                return log_debug_errno(SYNTHETIC_ERRNO(EIO), "Failed to allocate public key context");
+
+        if (EVP_PKEY_encrypt_init(ctx) <= 0)
+                return log_debug_errno(SYNTHETIC_ERRNO(EIO), "Failed to initialize public key context");
+
+        if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
+                return log_debug_errno(SYNTHETIC_ERRNO(EIO), "Failed to configure PKCS#1 padding");
+
+        if (EVP_PKEY_encrypt(ctx, NULL, &l, decrypted_key, decrypted_key_size) <= 0)
+                return log_debug_errno(SYNTHETIC_ERRNO(EIO), "Failed to determine encrypted key size");
+
+        b = malloc(l);
+        if (!b)
+                return -ENOMEM;
+
+        if (EVP_PKEY_encrypt(ctx, b, &l, decrypted_key, decrypted_key_size) <= 0)
+                return log_debug_errno(SYNTHETIC_ERRNO(EIO), "Failed to determine encrypted key size");
+
+        *ret_encrypt_key = TAKE_PTR(b);
+        *ret_encrypt_key_size = l;
+
+        return 0;
+}
+#endif