diff --git a/crypto/err/openssl.txt b/crypto/err/openssl.txt
index 4357cfb0068672aa90ba50ab0453ce0bf5e9557f..9ec000964a01b5d26fed325956b94fec2ce6f62b 100644
--- a/crypto/err/openssl.txt
+++ b/crypto/err/openssl.txt
@@ -893,6 +893,7 @@ RAND_F_RAND_DRBG_NEW:109:RAND_DRBG_new
 RAND_F_RAND_DRBG_RESEED:110:RAND_DRBG_reseed
 RAND_F_RAND_DRBG_RESTART:102:rand_drbg_restart
 RAND_F_RAND_DRBG_SET:104:RAND_DRBG_set
+RAND_F_RAND_DRBG_UNINSTANTIATE:118:RAND_DRBG_uninstantiate
 RAND_F_RAND_LOAD_FILE:111:RAND_load_file
 RAND_F_RAND_POOL_ADD:103:RAND_POOL_add
 RAND_F_RAND_POOL_ADD_BEGIN:113:RAND_POOL_add_begin
@@ -2258,6 +2259,7 @@ RAND_R_INTERNAL_ERROR:113:internal error
 RAND_R_IN_ERROR_STATE:114:in error state
 RAND_R_NOT_A_REGULAR_FILE:122:Not a regular file
 RAND_R_NOT_INSTANTIATED:115:not instantiated
+RAND_R_NO_DRBG_IMPLEMENTATION_SELECTED:128:no drbg implementation selected
 RAND_R_PERSONALISATION_STRING_TOO_LONG:116:personalisation string too long
 RAND_R_PRNG_NOT_SEEDED:100:PRNG not seeded
 RAND_R_RANDOM_POOL_OVERFLOW:125:random pool overflow
diff --git a/crypto/rand/drbg_ctr.c b/crypto/rand/drbg_ctr.c
index bb3acc88db0f5ab82abccb33ba8ee2b15225ec1a..3130e491dd39cb940d0e1bc19dfa0f83cebb3224 100644
--- a/crypto/rand/drbg_ctr.c
+++ b/crypto/rand/drbg_ctr.c
@@ -201,7 +201,7 @@ static void ctr_update(RAND_DRBG *drbg,
                        const unsigned char *in2, size_t in2len,
                        const unsigned char *nonce, size_t noncelen)
 {
-    RAND_DRBG_CTR *ctr = &drbg->ctr;
+    RAND_DRBG_CTR *ctr = &drbg->data.ctr;
 
     /* ks is already setup for correct key */
     inc_128(ctr);
@@ -236,12 +236,12 @@ static void ctr_update(RAND_DRBG *drbg,
     AES_set_encrypt_key(ctr->K, drbg->strength, &ctr->ks);
 }
 
-int ctr_instantiate(RAND_DRBG *drbg,
-                    const unsigned char *entropy, size_t entropylen,
-                    const unsigned char *nonce, size_t noncelen,
-                    const unsigned char *pers, size_t perslen)
+static int drbg_ctr_instantiate(RAND_DRBG *drbg,
+                                const unsigned char *entropy, size_t entropylen,
+                                const unsigned char *nonce, size_t noncelen,
+                                const unsigned char *pers, size_t perslen)
 {
-    RAND_DRBG_CTR *ctr = &drbg->ctr;
+    RAND_DRBG_CTR *ctr = &drbg->data.ctr;
 
     if (entropy == NULL)
         return 0;
@@ -253,9 +253,9 @@ int ctr_instantiate(RAND_DRBG *drbg,
     return 1;
 }
 
-int ctr_reseed(RAND_DRBG *drbg,
-               const unsigned char *entropy, size_t entropylen,
-               const unsigned char *adin, size_t adinlen)
+static int drbg_ctr_reseed(RAND_DRBG *drbg,
+                           const unsigned char *entropy, size_t entropylen,
+                           const unsigned char *adin, size_t adinlen)
 {
     if (entropy == NULL)
         return 0;
@@ -263,11 +263,11 @@ int ctr_reseed(RAND_DRBG *drbg,
     return 1;
 }
 
-int ctr_generate(RAND_DRBG *drbg,
-                 unsigned char *out, size_t outlen,
-                 const unsigned char *adin, size_t adinlen)
+static int drbg_ctr_generate(RAND_DRBG *drbg,
+                             unsigned char *out, size_t outlen,
+                             const unsigned char *adin, size_t adinlen)
 {
-    RAND_DRBG_CTR *ctr = &drbg->ctr;
+    RAND_DRBG_CTR *ctr = &drbg->data.ctr;
 
     if (adin != NULL && adinlen != 0) {
         ctr_update(drbg, adin, adinlen, NULL, 0, NULL, 0);
@@ -299,15 +299,22 @@ int ctr_generate(RAND_DRBG *drbg,
     return 1;
 }
 
-int ctr_uninstantiate(RAND_DRBG *drbg)
+static int drbg_ctr_uninstantiate(RAND_DRBG *drbg)
 {
-    OPENSSL_cleanse(&drbg->ctr, sizeof(drbg->ctr));
+    OPENSSL_cleanse(&drbg->data.ctr, sizeof(drbg->data.ctr));
     return 1;
 }
 
-int ctr_init(RAND_DRBG *drbg)
+static RAND_DRBG_METHOD drbg_ctr_meth = {
+    drbg_ctr_instantiate,
+    drbg_ctr_reseed,
+    drbg_ctr_generate,
+    drbg_ctr_uninstantiate
+};
+
+int drbg_ctr_init(RAND_DRBG *drbg)
 {
-    RAND_DRBG_CTR *ctr = &drbg->ctr;
+    RAND_DRBG_CTR *ctr = &drbg->data.ctr;
     size_t keylen;
 
     switch (drbg->nid) {
@@ -325,6 +332,8 @@ int ctr_init(RAND_DRBG *drbg)
         break;
     }
 
+    drbg->meth = &drbg_ctr_meth;
+
     ctr->keylen = keylen;
     drbg->strength = keylen * 8;
     drbg->seedlen = keylen + 16;
diff --git a/crypto/rand/drbg_lib.c b/crypto/rand/drbg_lib.c
index e33877e3ba9f7b01df3b6dcc68b36b0289fc1bff..795b098b367731272ed209c30d2d2bf34290aed1 100644
--- a/crypto/rand/drbg_lib.c
+++ b/crypto/rand/drbg_lib.c
@@ -124,7 +124,7 @@ int RAND_DRBG_set(RAND_DRBG *drbg, int nid, unsigned int flags)
     case NID_aes_128_ctr:
     case NID_aes_192_ctr:
     case NID_aes_256_ctr:
-        ret = ctr_init(drbg);
+        ret = drbg_ctr_init(drbg);
         break;
     }
 
@@ -172,7 +172,8 @@ void RAND_DRBG_free(RAND_DRBG *drbg)
     if (drbg == NULL)
         return;
 
-    ctr_uninstantiate(drbg);
+    if (drbg->meth != NULL)
+        drbg->meth->uninstantiate(drbg);
     CRYPTO_free_ex_data(CRYPTO_EX_INDEX_DRBG, drbg, &drbg->ex_data);
     OPENSSL_clear_free(drbg, sizeof(*drbg));
 }
@@ -196,6 +197,14 @@ int RAND_DRBG_instantiate(RAND_DRBG *drbg,
                 RAND_R_PERSONALISATION_STRING_TOO_LONG);
         goto end;
     }
+
+    if (drbg->meth == NULL)
+    {
+        RANDerr(RAND_F_RAND_DRBG_INSTANTIATE,
+                RAND_R_NO_DRBG_IMPLEMENTATION_SELECTED);
+        goto end;
+    }
+
     if (drbg->state != DRBG_UNINITIALISED) {
         RANDerr(RAND_F_RAND_DRBG_INSTANTIATE,
                 drbg->state == DRBG_ERROR ? RAND_R_IN_ERROR_STATE
@@ -223,7 +232,7 @@ int RAND_DRBG_instantiate(RAND_DRBG *drbg,
         }
     }
 
-    if (!ctr_instantiate(drbg, entropy, entropylen,
+    if (!drbg->meth->instantiate(drbg, entropy, entropylen,
                          nonce, noncelen, pers, perslen)) {
         RANDerr(RAND_F_RAND_DRBG_INSTANTIATE, RAND_R_ERROR_INSTANTIATING_DRBG);
         goto end;
@@ -267,11 +276,18 @@ end:
  */
 int RAND_DRBG_uninstantiate(RAND_DRBG *drbg)
 {
+    if (drbg->meth == NULL)
+    {
+        RANDerr(RAND_F_RAND_DRBG_UNINSTANTIATE,
+                RAND_R_NO_DRBG_IMPLEMENTATION_SELECTED);
+        return 0;
+    }
+
     /* Clear the entire drbg->ctr struct, then reset some important
      * members of the drbg->ctr struct (e.g. keysize, df_ks) to their
      * initial values.
      */
-    ctr_uninstantiate(drbg);
+    drbg->meth->uninstantiate(drbg);
     return RAND_DRBG_set(drbg, drbg->nid, drbg->flags);
 }
 
@@ -314,7 +330,7 @@ int RAND_DRBG_reseed(RAND_DRBG *drbg,
         goto end;
     }
 
-    if (!ctr_reseed(drbg, entropy, entropylen, adin, adinlen))
+    if (!drbg->meth->reseed(drbg, entropy, entropylen, adin, adinlen))
         goto end;
 
     drbg->state = DRBG_READY;
@@ -420,7 +436,7 @@ int rand_drbg_restart(RAND_DRBG *drbg,
              * entropy from the trusted entropy source using get_entropy().
              * This is not a reseeding in the strict sense of NIST SP 800-90A.
              */
-            ctr_reseed(drbg, adin, adinlen, NULL, 0);
+            drbg->meth->reseed(drbg, adin, adinlen, NULL, 0);
         } else if (reseeded == 0) {
             /* do a full reseeding if it has not been done yet above */
             RAND_DRBG_reseed(drbg, NULL, 0);
@@ -507,7 +523,7 @@ int RAND_DRBG_generate(RAND_DRBG *drbg, unsigned char *out, size_t outlen,
         adinlen = 0;
     }
 
-    if (!ctr_generate(drbg, out, outlen, adin, adinlen)) {
+    if (!drbg->meth->generate(drbg, out, outlen, adin, adinlen)) {
         drbg->state = DRBG_ERROR;
         RANDerr(RAND_F_RAND_DRBG_GENERATE, RAND_R_GENERATE_ERROR);
         return 0;
diff --git a/crypto/rand/rand_err.c b/crypto/rand/rand_err.c
index dc6140c07538ba2c4dfeef58be2e03c44b3ea4f3..ac70b4a2e01fb3a5a0a8846a8dc095836f73ee39 100644
--- a/crypto/rand/rand_err.c
+++ b/crypto/rand/rand_err.c
@@ -27,6 +27,8 @@ static const ERR_STRING_DATA RAND_str_functs[] = {
     {ERR_PACK(ERR_LIB_RAND, RAND_F_RAND_DRBG_RESEED, 0), "RAND_DRBG_reseed"},
     {ERR_PACK(ERR_LIB_RAND, RAND_F_RAND_DRBG_RESTART, 0), "rand_drbg_restart"},
     {ERR_PACK(ERR_LIB_RAND, RAND_F_RAND_DRBG_SET, 0), "RAND_DRBG_set"},
+    {ERR_PACK(ERR_LIB_RAND, RAND_F_RAND_DRBG_UNINSTANTIATE, 0),
+     "RAND_DRBG_uninstantiate"},
     {ERR_PACK(ERR_LIB_RAND, RAND_F_RAND_LOAD_FILE, 0), "RAND_load_file"},
     {ERR_PACK(ERR_LIB_RAND, RAND_F_RAND_POOL_ADD, 0), "RAND_POOL_add"},
     {ERR_PACK(ERR_LIB_RAND, RAND_F_RAND_POOL_ADD_BEGIN, 0),
@@ -76,6 +78,8 @@ static const ERR_STRING_DATA RAND_str_reasons[] = {
     {ERR_PACK(ERR_LIB_RAND, 0, RAND_R_NOT_A_REGULAR_FILE),
     "Not a regular file"},
     {ERR_PACK(ERR_LIB_RAND, 0, RAND_R_NOT_INSTANTIATED), "not instantiated"},
+    {ERR_PACK(ERR_LIB_RAND, 0, RAND_R_NO_DRBG_IMPLEMENTATION_SELECTED),
+    "no drbg implementation selected"},
     {ERR_PACK(ERR_LIB_RAND, 0, RAND_R_PERSONALISATION_STRING_TOO_LONG),
     "personalisation string too long"},
     {ERR_PACK(ERR_LIB_RAND, 0, RAND_R_PRNG_NOT_SEEDED), "PRNG not seeded"},
diff --git a/crypto/rand/rand_lcl.h b/crypto/rand/rand_lcl.h
index 9044981bbb89d781da007f928c2e872a58390391..1a09118546f9caddca172f64a201a0ac81502acd 100644
--- a/crypto/rand/rand_lcl.h
+++ b/crypto/rand/rand_lcl.h
@@ -54,6 +54,42 @@ typedef enum drbg_status_e {
 } DRBG_STATUS;
 
 
+/* intantiate */
+typedef int (*RAND_DRBG_instantiate_fn)(RAND_DRBG *ctx,
+                                        const unsigned char *ent,
+                                        size_t entlen,
+                                        const unsigned char *nonce,
+                                        size_t noncelen,
+                                        const unsigned char *pers,
+                                        size_t perslen);
+/* reseed */
+typedef int (*RAND_DRBG_reseed_fn)(RAND_DRBG *ctx,
+                                   const unsigned char *ent,
+                                   size_t entlen,
+                                   const unsigned char *adin,
+                                   size_t adinlen);
+/* generat output */
+typedef int (*RAND_DRBG_generate_fn)(RAND_DRBG *ctx,
+                                     unsigned char *out,
+                                     size_t outlen,
+                                     const unsigned char *adin,
+                                     size_t adinlen);
+/* uninstantiate */
+typedef int (*RAND_DRBG_uninstantiate_fn)(RAND_DRBG *ctx);
+
+
+/*
+ * The DRBG methods
+ */
+
+typedef struct rand_drbg_method_st {
+    RAND_DRBG_instantiate_fn instantiate;
+    RAND_DRBG_reseed_fn reseed;
+    RAND_DRBG_generate_fn generate;
+    RAND_DRBG_uninstantiate_fn uninstantiate;
+} RAND_DRBG_METHOD;
+
+
 /*
  * The state of a DRBG AES-CTR.
  */
@@ -96,7 +132,7 @@ struct rand_drbg_st {
     /*
      * The following parameters are setup by the per-type "init" function.
      *
-     * Currently the only type is CTR_DRBG, its init function is ctr_init().
+     * Currently the only type is CTR_DRBG, its init function is drbg_ctr_init().
      *
      * The parameters are closely related to the ones described in
      * section '10.2.1 CTR_DRBG' of [NIST SP 800-90Ar1], with one
@@ -148,8 +184,13 @@ struct rand_drbg_st {
     /* Application data, mainly used in the KATs. */
     CRYPTO_EX_DATA ex_data;
 
-    /* Implementation specific structures; was a union, but inline for now */
-    RAND_DRBG_CTR ctr;
+    /* Implementation specific data (currently only one implementation) */
+    union {
+        RAND_DRBG_CTR ctr;
+    } data;
+
+    /* Implementation specific methods */
+    RAND_DRBG_METHOD *meth;
 
     /* Callback functions.  See comments in rand_lib.c */
     RAND_DRBG_get_entropy_fn get_entropy;
@@ -179,18 +220,7 @@ void rand_drbg_cleanup_entropy(RAND_DRBG *drbg,
 int rand_drbg_restart(RAND_DRBG *drbg,
                       const unsigned char *buffer, size_t len, size_t entropy);
 
-/* DRBG functions implementing AES-CTR */
-int ctr_init(RAND_DRBG *drbg);
-int ctr_uninstantiate(RAND_DRBG *drbg);
-int ctr_instantiate(RAND_DRBG *drbg,
-                    const unsigned char *entropy, size_t entropylen,
-                    const unsigned char *nonce, size_t noncelen,
-                    const unsigned char *pers, size_t perslen);
-int ctr_reseed(RAND_DRBG *drbg,
-               const unsigned char *entropy, size_t entropylen,
-               const unsigned char *adin, size_t adinlen);
-int ctr_generate(RAND_DRBG *drbg,
-                 unsigned char *out, size_t outlen,
-                 const unsigned char *adin, size_t adinlen);
+/* initializes the AES-CTR DRBG implementation */
+int drbg_ctr_init(RAND_DRBG *drbg);
 
 #endif
diff --git a/include/openssl/randerr.h b/include/openssl/randerr.h
index b07ea233eb53be047e61548656197d500f2c76bc..b136ce87e1a6010ebe910f593c5f1fb02d58443b 100644
--- a/include/openssl/randerr.h
+++ b/include/openssl/randerr.h
@@ -33,6 +33,7 @@ int ERR_load_RAND_strings(void);
 # define RAND_F_RAND_DRBG_RESEED                          110
 # define RAND_F_RAND_DRBG_RESTART                         102
 # define RAND_F_RAND_DRBG_SET                             104
+# define RAND_F_RAND_DRBG_UNINSTANTIATE                   118
 # define RAND_F_RAND_LOAD_FILE                            111
 # define RAND_F_RAND_POOL_ADD                             103
 # define RAND_F_RAND_POOL_ADD_BEGIN                       113
@@ -65,6 +66,7 @@ int ERR_load_RAND_strings(void);
 # define RAND_R_IN_ERROR_STATE                            114
 # define RAND_R_NOT_A_REGULAR_FILE                        122
 # define RAND_R_NOT_INSTANTIATED                          115
+# define RAND_R_NO_DRBG_IMPLEMENTATION_SELECTED           128
 # define RAND_R_PERSONALISATION_STRING_TOO_LONG           116
 # define RAND_R_PRNG_NOT_SEEDED                           100
 # define RAND_R_RANDOM_POOL_OVERFLOW                      125
diff --git a/test/drbgtest.c b/test/drbgtest.c
index 68c169793c9987a5eed7d9fe4c6667eaf454ed5c..fcb4b2846010e1fccc9a7a35c55d1383694d4b8f 100644
--- a/test/drbgtest.c
+++ b/test/drbgtest.c
@@ -438,7 +438,7 @@ static int error_check(DRBG_SELFTEST_DATA *td)
         goto err;
 
     /* Standard says we have to check uninstantiate really zeroes */
-    if (!TEST_mem_eq(zero, sizeof(drbg->ctr), &drbg->ctr, sizeof(drbg->ctr)))
+    if (!TEST_mem_eq(zero, sizeof(drbg->data), &drbg->data, sizeof(drbg->data)))
         goto err;
 
     ret = 1;