diff --git a/crypto/rand/drbg_lib.c b/crypto/rand/drbg_lib.c
index 6aced40fd4..0560e3baa7 100644
--- a/crypto/rand/drbg_lib.c
+++ b/crypto/rand/drbg_lib.c
@@ -125,9 +125,9 @@ int RAND_DRBG_instantiate(RAND_DRBG *drbg,
                           const unsigned char *pers, size_t perslen)
 {
     unsigned char *nonce = NULL, *entropy = NULL;
-    size_t noncelen = 0, entlen = 0;
+    size_t noncelen = 0, entropylen = 0;
 
-    if (perslen > drbg->max_pers) {
+    if (perslen > drbg->max_perslen) {
         RANDerr(RAND_F_RAND_DRBG_INSTANTIATE,
                 RAND_R_PERSONALISATION_STRING_TOO_LONG);
         goto end;
@@ -141,23 +141,23 @@ int RAND_DRBG_instantiate(RAND_DRBG *drbg,
 
     drbg->state = DRBG_ERROR;
     if (drbg->get_entropy != NULL)
-        entlen = drbg->get_entropy(drbg, &entropy, drbg->strength,
-                                   drbg->min_entropy, drbg->max_entropy);
-    if (entlen < drbg->min_entropy || entlen > drbg->max_entropy) {
+        entropylen = drbg->get_entropy(drbg, &entropy, drbg->strength,
+                                   drbg->min_entropylen, drbg->max_entropylen);
+    if (entropylen < drbg->min_entropylen || entropylen > drbg->max_entropylen) {
         RANDerr(RAND_F_RAND_DRBG_INSTANTIATE, RAND_R_ERROR_RETRIEVING_ENTROPY);
         goto end;
     }
 
-    if (drbg->max_nonce > 0 && drbg->get_nonce != NULL) {
+    if (drbg->max_noncelen > 0 && drbg->get_nonce != NULL) {
         noncelen = drbg->get_nonce(drbg, &nonce, drbg->strength / 2,
-                                   drbg->min_nonce, drbg->max_nonce);
-        if (noncelen < drbg->min_nonce || noncelen > drbg->max_nonce) {
+                                   drbg->min_noncelen, drbg->max_noncelen);
+        if (noncelen < drbg->min_noncelen || noncelen > drbg->max_noncelen) {
             RANDerr(RAND_F_RAND_DRBG_INSTANTIATE, RAND_R_ERROR_RETRIEVING_NONCE);
             goto end;
         }
     }
 
-    if (!ctr_instantiate(drbg, entropy, entlen,
+    if (!ctr_instantiate(drbg, entropy, entropylen,
                          nonce, noncelen, pers, perslen)) {
         RANDerr(RAND_F_RAND_DRBG_INSTANTIATE, RAND_R_ERROR_INSTANTIATING_DRBG);
         goto end;
@@ -195,7 +195,7 @@ int RAND_DRBG_reseed(RAND_DRBG *drbg,
                      const unsigned char *adin, size_t adinlen)
 {
     unsigned char *entropy = NULL;
-    size_t entlen = 0;
+    size_t entropylen = 0;
 
     if (drbg->state == DRBG_ERROR) {
         RANDerr(RAND_F_RAND_DRBG_RESEED, RAND_R_IN_ERROR_STATE);
@@ -208,21 +208,21 @@ int RAND_DRBG_reseed(RAND_DRBG *drbg,
 
     if (adin == NULL)
         adinlen = 0;
-    else if (adinlen > drbg->max_adin) {
+    else if (adinlen > drbg->max_adinlen) {
         RANDerr(RAND_F_RAND_DRBG_RESEED, RAND_R_ADDITIONAL_INPUT_TOO_LONG);
         return 0;
     }
 
     drbg->state = DRBG_ERROR;
     if (drbg->get_entropy != NULL)
-        entlen = drbg->get_entropy(drbg, &entropy, drbg->strength,
-                                   drbg->min_entropy, drbg->max_entropy);
-    if (entlen < drbg->min_entropy || entlen > drbg->max_entropy) {
+        entropylen = drbg->get_entropy(drbg, &entropy, drbg->strength,
+                                   drbg->min_entropylen, drbg->max_entropylen);
+    if (entropylen < drbg->min_entropylen || entropylen > drbg->max_entropylen) {
         RANDerr(RAND_F_RAND_DRBG_RESEED, RAND_R_ERROR_RETRIEVING_ENTROPY);
         goto end;
     }
 
-    if (!ctr_reseed(drbg, entropy, entlen, adin, adinlen))
+    if (!ctr_reseed(drbg, entropy, entropylen, adin, adinlen))
         goto end;
     drbg->state = DRBG_READY;
     drbg->reseed_counter = 1;
@@ -256,7 +256,7 @@ int RAND_DRBG_generate(RAND_DRBG *drbg, unsigned char *out, size_t outlen,
         RANDerr(RAND_F_RAND_DRBG_GENERATE, RAND_R_REQUEST_TOO_LARGE_FOR_DRBG);
         return 0;
     }
-    if (adinlen > drbg->max_adin) {
+    if (adinlen > drbg->max_adinlen) {
         RANDerr(RAND_F_RAND_DRBG_GENERATE, RAND_R_ADDITIONAL_INPUT_TOO_LONG);
         return 0;
     }
diff --git a/crypto/rand/drbg_rand.c b/crypto/rand/drbg_rand.c
index 934679e315..83f1ad876f 100644
--- a/crypto/rand/drbg_rand.c
+++ b/crypto/rand/drbg_rand.c
@@ -237,29 +237,29 @@ static void ctr_update(RAND_DRBG *drbg,
 }
 
 int ctr_instantiate(RAND_DRBG *drbg,
-                    const unsigned char *ent, size_t entlen,
+                    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;
 
-    if (ent == NULL)
+    if (entropy == NULL)
         return 0;
 
     memset(ctr->K, 0, sizeof(ctr->K));
     memset(ctr->V, 0, sizeof(ctr->V));
     AES_set_encrypt_key(ctr->K, drbg->strength, &ctr->ks);
-    ctr_update(drbg, ent, entlen, pers, perslen, nonce, noncelen);
+    ctr_update(drbg, entropy, entropylen, pers, perslen, nonce, noncelen);
     return 1;
 }
 
 int ctr_reseed(RAND_DRBG *drbg,
-               const unsigned char *ent, size_t entlen,
+               const unsigned char *entropy, size_t entropylen,
                const unsigned char *adin, size_t adinlen)
 {
-    if (ent == NULL)
+    if (entropy == NULL)
         return 0;
-    ctr_update(drbg, ent, entlen, adin, adinlen, NULL, 0);
+    ctr_update(drbg, entropy, entropylen, adin, adinlen, NULL, 0);
     return 1;
 }
 
@@ -340,20 +340,20 @@ int ctr_init(RAND_DRBG *drbg)
         /* Set key schedule for df_key */
         AES_set_encrypt_key(df_key, drbg->strength, &ctr->df_ks);
 
-        drbg->min_entropy = ctr->keylen;
-        drbg->max_entropy = DRBG_MAX_LENGTH;
-        drbg->min_nonce = drbg->min_entropy / 2;
-        drbg->max_nonce = DRBG_MAX_LENGTH;
-        drbg->max_pers = DRBG_MAX_LENGTH;
-        drbg->max_adin = DRBG_MAX_LENGTH;
+        drbg->min_entropylen = ctr->keylen;
+        drbg->max_entropylen = DRBG_MAX_LENGTH;
+        drbg->min_noncelen = drbg->min_entropylen / 2;
+        drbg->max_noncelen = DRBG_MAX_LENGTH;
+        drbg->max_perslen = DRBG_MAX_LENGTH;
+        drbg->max_adinlen = DRBG_MAX_LENGTH;
     } else {
-        drbg->min_entropy = drbg->seedlen;
-        drbg->max_entropy = drbg->seedlen;
+        drbg->min_entropylen = drbg->seedlen;
+        drbg->max_entropylen = drbg->seedlen;
         /* Nonce not used */
-        drbg->min_nonce = 0;
-        drbg->max_nonce = 0;
-        drbg->max_pers = drbg->seedlen;
-        drbg->max_adin = drbg->seedlen;
+        drbg->min_noncelen = 0;
+        drbg->max_noncelen = 0;
+        drbg->max_perslen = drbg->seedlen;
+        drbg->max_adinlen = drbg->seedlen;
     }
 
     drbg->max_request = 1 << 16;
diff --git a/crypto/rand/rand_lcl.h b/crypto/rand/rand_lcl.h
index e60f619d61..0d85934533 100644
--- a/crypto/rand/rand_lcl.h
+++ b/crypto/rand/rand_lcl.h
@@ -103,12 +103,28 @@ struct rand_drbg_st {
     int size;
     unsigned char *randomness;
 
-    /* These parameters are setup by the per-type "init" function. */
+    /* 
+     * The following parameters are setup by the per-type "init" function.
+     *
+     * Currently the only type is CTR_DRBG, its init function is 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
+     * crucial difference: In the NIST standard, all counts are given
+     * in bits, whereas in OpenSSL entropy counts are given in bits 
+     * and buffer lengths are given in bytes.
+     * 
+     * Since this difference has lead to some confusion in the past,
+     * (see [GitHub Issue #2443], formerly [rt.openssl.org #4055])
+     * the 'len' suffix has been added to all buffer sizes for 
+     * clarification.
+     */
+    
     int strength;
     size_t max_request;
-    size_t min_entropy, max_entropy;
-    size_t min_nonce, max_nonce;
-    size_t max_pers, max_adin;
+    size_t min_entropylen, max_entropylen;
+    size_t min_noncelen, max_noncelen;
+    size_t max_perslen, max_adinlen;
     unsigned int reseed_counter;
     unsigned int reseed_interval;
     size_t seedlen;
@@ -153,11 +169,11 @@ size_t drbg_entropy_from_system(RAND_DRBG *drbg,
 int ctr_init(RAND_DRBG *drbg);
 int ctr_uninstantiate(RAND_DRBG *drbg);
 int ctr_instantiate(RAND_DRBG *drbg,
-                    const unsigned char *ent, size_t entlen,
+                    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 *ent, size_t entlen,
+               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,
diff --git a/test/drbgtest.c b/test/drbgtest.c
index 2363b5025c..7d33c3035d 100644
--- a/test/drbgtest.c
+++ b/test/drbgtest.c
@@ -26,16 +26,16 @@ typedef struct drbg_selftest_data_st {
     unsigned int flags;
 
     /* KAT data for no PR */
-    const unsigned char *ent;
-    size_t entlen;
+    const unsigned char *entropy;
+    size_t entropylen;
     const unsigned char *nonce;
     size_t noncelen;
     const unsigned char *pers;
     size_t perslen;
     const unsigned char *adin;
     size_t adinlen;
-    const unsigned char *entreseed;
-    size_t entreseedlen;
+    const unsigned char *entropyreseed;
+    size_t entropyreseedlen;
     const unsigned char *adinreseed;
     size_t adinreseedlen;
     const unsigned char *adin2;
@@ -46,20 +46,20 @@ typedef struct drbg_selftest_data_st {
     size_t kat2len;
 
     /* KAT data for PR */
-    const unsigned char *ent_pr;
-    size_t entlen_pr;
+    const unsigned char *entropy_pr;
+    size_t entropylen_pr;
     const unsigned char *nonce_pr;
     size_t noncelen_pr;
     const unsigned char *pers_pr;
     size_t perslen_pr;
     const unsigned char *adin_pr;
     size_t adinlen_pr;
-    const unsigned char *entpr_pr;
-    size_t entprlen_pr;
+    const unsigned char *entropypr_pr;
+    size_t entropyprlen_pr;
     const unsigned char *ading_pr;
     size_t adinglen_pr;
-    const unsigned char *entg_pr;
-    size_t entglen_pr;
+    const unsigned char *entropyg_pr;
+    size_t entropyglen_pr;
     const unsigned char *kat_pr;
     size_t katlen_pr;
     const unsigned char *kat2_pr;
@@ -106,9 +106,9 @@ static int app_data_index;
  * Test context data, attached as EXDATA to the RAND_DRBG
  */
 typedef struct test_ctx_st {
-    const unsigned char *ent;
-    size_t entlen;
-    int entcnt;
+    const unsigned char *entropy;
+    size_t entropylen;
+    int entropycnt;
     const unsigned char *nonce;
     size_t noncelen;
     int noncecnt;
@@ -119,9 +119,9 @@ static size_t kat_entropy(RAND_DRBG *drbg, unsigned char **pout,
 {
     TEST_CTX *t = (TEST_CTX *)RAND_DRBG_get_ex_data(drbg, app_data_index);
 
-    t->entcnt++;
-    *pout = (unsigned char *)t->ent;
-    return t->entlen;
+    t->entropycnt++;
+    *pout = (unsigned char *)t->entropy;
+    return t->entropylen;
 }
 
 static size_t kat_nonce(RAND_DRBG *drbg, unsigned char **pout,
@@ -164,8 +164,8 @@ static int single_kat(DRBG_SELFTEST_DATA *td)
         goto err;
     }
     memset(&t, 0, sizeof(t));
-    t.ent = td->ent;
-    t.entlen = td->entlen;
+    t.entropy = td->entropy;
+    t.entropylen = td->entropylen;
     t.nonce = td->nonce;
     t.noncelen = td->noncelen;
     RAND_DRBG_set_ex_data(drbg, app_data_index, &t);
@@ -177,8 +177,8 @@ static int single_kat(DRBG_SELFTEST_DATA *td)
         failures++;
 
     /* Reseed DRBG with test entropy and additional input */
-    t.ent = td->entreseed;
-    t.entlen = td->entreseedlen;
+    t.entropy = td->entropyreseed;
+    t.entropylen = td->entropyreseedlen;
     if (!TEST_true(RAND_DRBG_reseed(drbg, td->adinreseed, td->adinreseedlen)
             || !TEST_true(RAND_DRBG_generate(drbg, buff, td->kat2len, 0,
                                              td->adin2, td->adin2len))
@@ -195,11 +195,11 @@ static int single_kat(DRBG_SELFTEST_DATA *td)
                                                   kat_nonce, NULL)))
         failures++;
     RAND_DRBG_set_ex_data(drbg, app_data_index, &t);
-    t.ent = td->ent_pr;
-    t.entlen = td->entlen_pr;
+    t.entropy = td->entropy_pr;
+    t.entropylen = td->entropylen_pr;
     t.nonce = td->nonce_pr;
     t.noncelen = td->noncelen_pr;
-    t.entcnt = 0;
+    t.entropycnt = 0;
     t.noncecnt = 0;
     if (!TEST_true(RAND_DRBG_instantiate(drbg, td->pers_pr, td->perslen_pr)))
         failures++;
@@ -208,8 +208,8 @@ static int single_kat(DRBG_SELFTEST_DATA *td)
      * Now generate with PR: we need to supply entropy as this will
      * perform a reseed operation.
      */
-    t.ent = td->entpr_pr;
-    t.entlen = td->entprlen_pr;
+    t.entropy = td->entropypr_pr;
+    t.entropylen = td->entropyprlen_pr;
     if (!TEST_true(RAND_DRBG_generate(drbg, buff, td->katlen_pr, 1,
                                       td->adin_pr, td->adinlen_pr))
             || !TEST_mem_eq(td->kat_pr, td->katlen_pr, buff, td->katlen_pr))
@@ -218,8 +218,8 @@ static int single_kat(DRBG_SELFTEST_DATA *td)
     /*
      * Now generate again with PR: supply new entropy again.
      */
-    t.ent = td->entg_pr;
-    t.entlen = td->entglen_pr;
+    t.entropy = td->entropyg_pr;
+    t.entropylen = td->entropyglen_pr;
 
     if (!TEST_true(RAND_DRBG_generate(drbg, buff, td->kat2len_pr, 1,
                                       td->ading_pr, td->adinglen_pr))
@@ -243,11 +243,11 @@ static int init(RAND_DRBG *drbg, DRBG_SELFTEST_DATA *td, TEST_CTX *t)
                                                   kat_nonce, NULL)))
         return 0;
     RAND_DRBG_set_ex_data(drbg, app_data_index, t);
-    t->ent = td->ent;
-    t->entlen = td->entlen;
+    t->entropy = td->entropy;
+    t->entropylen = td->entropylen;
     t->nonce = td->nonce;
     t->noncelen = td->noncelen;
-    t->entcnt = 0;
+    t->entropycnt = 0;
     t->noncecnt = 0;
     return 1;
 }
@@ -286,7 +286,7 @@ static int error_check(DRBG_SELFTEST_DATA *td)
 
     /* Test detection of too large personlisation string */
     if (!init(drbg, td, &t)
-            || RAND_DRBG_instantiate(drbg, td->pers, drbg->max_pers + 1) > 0)
+            || RAND_DRBG_instantiate(drbg, td->pers, drbg->max_perslen + 1) > 0)
         goto err;
 
     /*
@@ -294,7 +294,7 @@ static int error_check(DRBG_SELFTEST_DATA *td)
      */
 
     /* Test entropy source failure detecion: i.e. returns no data */
-    t.entlen = 0;
+    t.entropylen = 0;
     if (TEST_int_le(RAND_DRBG_instantiate(drbg, td->pers, td->perslen), 0))
         goto err;
 
@@ -305,14 +305,14 @@ static int error_check(DRBG_SELFTEST_DATA *td)
         goto err;
 
     /* Test insufficient entropy */
-    t.entlen = drbg->min_entropy - 1;
+    t.entropylen = drbg->min_entropylen - 1;
     if (!init(drbg, td, &t)
             || RAND_DRBG_instantiate(drbg, td->pers, td->perslen) > 0
             || !uninstantiate(drbg))
         goto err;
 
     /* Test too much entropy */
-    t.entlen = drbg->max_entropy + 1;
+    t.entropylen = drbg->max_entropylen + 1;
     if (!init(drbg, td, &t)
             || RAND_DRBG_instantiate(drbg, td->pers, td->perslen) > 0
             || !uninstantiate(drbg))
@@ -323,8 +323,8 @@ static int error_check(DRBG_SELFTEST_DATA *td)
      */
 
     /* Test too small nonce */
-    if (drbg->min_nonce) {
-        t.noncelen = drbg->min_nonce - 1;
+    if (drbg->min_noncelen) {
+        t.noncelen = drbg->min_noncelen - 1;
         if (!init(drbg, td, &t)
                 || RAND_DRBG_instantiate(drbg, td->pers, td->perslen) > 0
                 || !uninstantiate(drbg))
@@ -332,8 +332,8 @@ static int error_check(DRBG_SELFTEST_DATA *td)
     }
 
     /* Test too large nonce */
-    if (drbg->max_nonce) {
-        t.noncelen = drbg->max_nonce + 1;
+    if (drbg->max_noncelen) {
+        t.noncelen = drbg->max_noncelen + 1;
         if (!init(drbg, td, &t)
                 || RAND_DRBG_instantiate(drbg, td->pers, td->perslen) > 0
                 || !uninstantiate(drbg))
@@ -353,14 +353,14 @@ static int error_check(DRBG_SELFTEST_DATA *td)
 
     /* Try too large additional input */
     if (!TEST_false(RAND_DRBG_generate(drbg, buff, td->exlen, 0,
-                                       td->adin, drbg->max_adin + 1)))
+                                       td->adin, drbg->max_adinlen + 1)))
         goto err;
 
     /*
      * Check prediction resistance request fails if entropy source
      * failure.
      */
-    t.entlen = 0;
+    t.entropylen = 0;
     if (TEST_false(RAND_DRBG_generate(drbg, buff, td->exlen, 1,
                                       td->adin, td->adinlen))
             || !uninstantiate(drbg))
@@ -373,10 +373,10 @@ static int error_check(DRBG_SELFTEST_DATA *td)
     drbg->reseed_counter = drbg->reseed_interval;
 
     /* Generate output and check entropy has been requested for reseed */
-    t.entcnt = 0;
+    t.entropycnt = 0;
     if (!TEST_true(RAND_DRBG_generate(drbg, buff, td->exlen, 0,
                                       td->adin, td->adinlen))
-            || !TEST_int_eq(t.entcnt, 1)
+            || !TEST_int_eq(t.entropycnt, 1)
             || !TEST_int_eq(drbg->reseed_counter, reseed_counter_tmp + 1)
             || !uninstantiate(drbg))
         goto err;
@@ -385,7 +385,7 @@ static int error_check(DRBG_SELFTEST_DATA *td)
      * Check prediction resistance request fails if entropy source
      * failure.
      */
-    t.entlen = 0;
+    t.entropylen = 0;
     if (!TEST_false(RAND_DRBG_generate(drbg, buff, td->exlen, 1,
                                        td->adin, td->adinlen))
             || !uninstantiate(drbg))
@@ -398,10 +398,10 @@ static int error_check(DRBG_SELFTEST_DATA *td)
     drbg->reseed_counter = drbg->reseed_interval;
 
     /* Generate output and check entropy has been requested for reseed */
-    t.entcnt = 0;
+    t.entropycnt = 0;
     if (!TEST_true(RAND_DRBG_generate(drbg, buff, td->exlen, 0,
                                       td->adin, td->adinlen))
-            || !TEST_int_eq(t.entcnt, 1)
+            || !TEST_int_eq(t.entropycnt, 1)
             || !TEST_int_eq(drbg->reseed_counter, reseed_counter_tmp + 1)
             || !uninstantiate(drbg))
         goto err;
@@ -412,11 +412,11 @@ static int error_check(DRBG_SELFTEST_DATA *td)
 
     /* Test explicit reseed with too large additional input */
     if (!init(drbg, td, &t)
-            || RAND_DRBG_reseed(drbg, td->adin, drbg->max_adin + 1) > 0)
+            || RAND_DRBG_reseed(drbg, td->adin, drbg->max_adinlen + 1) > 0)
         goto err;
 
     /* Test explicit reseed with entropy source failure */
-    t.entlen = 0;
+    t.entropylen = 0;
     if (!TEST_int_le(RAND_DRBG_reseed(drbg, td->adin, td->adinlen), 0)
             || !uninstantiate(drbg))
         goto err;
@@ -424,7 +424,7 @@ static int error_check(DRBG_SELFTEST_DATA *td)
     /* Test explicit reseed with too much entropy */
     if (!init(drbg, td, &t))
         goto err;
-    t.entlen = drbg->max_entropy + 1;
+    t.entropylen = drbg->max_entropylen + 1;
     if (!TEST_int_le(RAND_DRBG_reseed(drbg, td->adin, td->adinlen), 0)
             || !uninstantiate(drbg))
         goto err;
@@ -432,7 +432,7 @@ static int error_check(DRBG_SELFTEST_DATA *td)
     /* Test explicit reseed with too little entropy */
     if (!init(drbg, td, &t))
         goto err;
-    t.entlen = drbg->min_entropy - 1;
+    t.entropylen = drbg->min_entropylen - 1;
     if (!TEST_int_le(RAND_DRBG_reseed(drbg, td->adin, td->adinlen), 0)
             || !uninstantiate(drbg))
         goto err;