diff --git a/libp2p/crypto/crypto.nim b/libp2p/crypto/crypto.nim
index 83401f4..49416d5 100644
--- a/libp2p/crypto/crypto.nim
+++ b/libp2p/crypto/crypto.nim
@@ -8,14 +8,15 @@
 ## those terms.
 
 ## This module implements Public Key and Private Key interface for libp2p.
-import strutils
 import rsa, ecnist, ed25519/ed25519, secp
-import ../protobuf/minprotobuf, ../vbuffer
+import ../protobuf/minprotobuf, ../vbuffer, ../multihash, ../multicodec
 import nimcrypto/[rijndael, blowfish, sha, sha2, hash, hmac, utils]
 
 # This is workaround for Nim's `import` bug
 export rijndael, blowfish, sha, sha2, hash, hmac, utils
 
+from strutils import split
+
 type
   PKScheme* = enum
     RSA = 0,
@@ -463,7 +464,7 @@ proc verify*(sig: Signature, message: openarray[byte],
     if signature.init(sig.data):
       result = signature.verify(message, key.skkey)
 
-template makeSecret(buffer, hmactype, secret, seed) =
+template makeSecret(buffer, hmactype, secret, seed: untyped) {.dirty.}=
   var ctx: hmactype
   var j = 0
   # We need to strip leading zeros, because Go bigint serialization do it.
@@ -489,16 +490,16 @@ template makeSecret(buffer, hmactype, secret, seed) =
     ctx.update(a.data)
     a = ctx.finish()
 
-proc stretchKeys*(cipherScheme: CipherScheme, hashScheme: DigestSheme,
-                  secret: openarray[byte]): Secret =
+proc stretchKeys*(cipherType: string, hashType: string,
+                  sharedSecret: seq[byte]): Secret =
   ## Expand shared secret to cryptographic keys.
-  if cipherScheme == Aes128:
+  if cipherType == "AES-128":
     result.ivsize = aes128.sizeBlock
     result.keysize = aes128.sizeKey
-  elif cipherScheme == Aes256:
+  elif cipherType == "AES-256":
     result.ivsize = aes256.sizeBlock
     result.keysize = aes256.sizeKey
-  elif cipherScheme == Blowfish:
+  elif cipherType == "BLOWFISH":
     result.ivsize = 8
     result.keysize = 32
 
@@ -507,12 +508,12 @@ proc stretchKeys*(cipherScheme: CipherScheme, hashScheme: DigestSheme,
   let length = result.ivsize + result.keysize + result.macsize
   result.data = newSeq[byte](2 * length)
 
-  if hashScheme == Sha256:
-    makeSecret(result.data, HMAC[sha256], secret, seed)
-  elif hashScheme == Sha512:
-    makeSecret(result.data, HMAC[sha512], secret, seed)
-  elif hashScheme == Sha1:
-    makeSecret(result.data, HMAC[sha1], secret, seed)
+  if hashType == "SHA256":
+    makeSecret(result.data, HMAC[sha256], sharedSecret, seed)
+  elif hashType == "SHA512":
+    makeSecret(result.data, HMAC[sha512], sharedSecret, seed)
+  elif hashType == "SHA1":
+    makeSecret(result.data, HMAC[sha1], sharedSecret, seed)
 
 template goffset*(secret, id, o: untyped): untyped =
   id * (len(secret.data) shr 1) + o
@@ -561,11 +562,27 @@ proc ephemeral*(scheme: ECDHEScheme): KeyPair =
   result.seckey.eckey = keypair.seckey
   result.pubkey.eckey = keypair.pubkey
 
+proc ephemeral*(scheme: string): KeyPair {.inline.} =
+  ## Generate ephemeral keys used to perform ECDHE using string encoding.
+  ##
+  ## Currently supported encoding strings are P-256, P-384, P-521, if encoding
+  ## string is not supported P-521 key will be generated.
+  if scheme == "P-256":
+    result = ephemeral(Secp256r1)
+  elif scheme == "P-384":
+    result = ephemeral(Secp384r1)
+  elif scheme == "P-521":
+    result = ephemeral(Secp521r1)
+  else:
+    result = ephemeral(Secp521r1)
+
 proc makeSecret*(remoteEPublic: PublicKey, localEPrivate: PrivateKey,
                  data: var openarray[byte]): int =
   ## Calculate shared secret using remote ephemeral public key
   ## ``remoteEPublic`` and local ephemeral private key ``localEPrivate`` and
-  ## store shared secret to ``data``
+  ## store shared secret to ``data``.
+  ##
+  ## Note this procedure supports only ECDSA keys.
   ##
   ## Returns number of bytes (octets) used to store shared secret data, or
   ## ``0`` on error.
@@ -573,6 +590,19 @@ proc makeSecret*(remoteEPublic: PublicKey, localEPrivate: PrivateKey,
     if localEPrivate.scheme == remoteEPublic.scheme:
       result = toSecret(remoteEPublic.eckey, localEPrivate.eckey, data)
 
+proc getSecret*(remoteEPublic: PublicKey,
+                localEPrivate: PrivateKey): seq[byte] =
+  ## Calculate shared secret using remote ephemeral public key
+  ## ``remoteEPublic`` and local ephemeral private key ``localEPrivate`` and
+  ## store shared secret to ``data``.
+  ##
+  ## Note this procedure supports only ECDSA keys.
+  ##
+  ## Returns shared secret on success.
+  if remoteEPublic.scheme == ECDSA:
+    if localEPrivate.scheme == remoteEPublic.scheme:
+      result = getSecret(remoteEPublic.eckey, localEPrivate.eckey)
+
 proc getOrder*(remotePubkey, localNonce: openarray[byte],
                localPubkey, remoteNonce: openarray[byte]): int =
   ## Compare values and calculate `order` parameter.
@@ -585,10 +615,16 @@ proc getOrder*(remotePubkey, localNonce: openarray[byte],
   ctx.update(localPubkey)
   ctx.update(remoteNonce)
   var digest2 = ctx.finish()
-  var diff = 0
-  for i in 0 ..< len(digest1.data):
-    diff = int(digest1.data[i]) - int(digest2.data[i])
-    result = (result and -not(diff)) or diff
+  var mh1 = MultiHash.init(multiCodec("sha2-256"), digest1)
+  var mh2 = MultiHash.init(multiCodec("sha2-256"), digest2)
+  for i in 0 ..< len(mh1.data.buffer):
+    result = int(mh1.data.buffer[i]) - int(mh2.data.buffer[i])
+    if result != 0:
+      if result > 0:
+        result = -1
+      elif result > 0:
+        result = 1
+      break
 
 proc selectBest*(order: int, p1, p2: string): string =
   ## Determines which algorithm to use from list `p1` and `p2`.
@@ -610,10 +646,14 @@ proc selectBest*(order: int, p1, p2: string): string =
     for selement in s:
       if felement == selement:
         result = felement
-        break
+        return
 
 proc createProposal*(nonce, pubkey: openarray[byte],
                      exchanges, ciphers, hashes: string): seq[byte] =
+  ## Create SecIO proposal message using random ``nonce``, local public key
+  ## ``pubkey``, comma-delimieted list of supported exchange schemes
+  ## ``exchanges``, comma-delimeted list of supported ciphers ``ciphers`` and
+  ## comma-delimeted list of supported hashes ``hashes``.
   var msg = initProtoBuffer({WithUint32BeLength})
   msg.write(initProtoField(1, nonce))
   msg.write(initProtoField(2, pubkey))
@@ -623,13 +663,42 @@ proc createProposal*(nonce, pubkey: openarray[byte],
   msg.finish()
   shallowCopy(result, msg.buffer)
 
+proc decodeProposal*(message: seq[byte], nonce, pubkey: var seq[byte],
+                     exchanges, ciphers, hashes: var string): bool =
+  ## Parse incoming proposal message and decode remote random nonce ``nonce``,
+  ## remote public key ``pubkey``, comma-delimieted list of supported exchange
+  ## schemes ``exchanges``, comma-delimeted list of supported ciphers
+  ## ``ciphers`` and comma-delimeted list of supported hashes ``hashes``.
+  ##
+  ## Procedure returns ``true`` on success and ``false`` on error.
+  var pb = initProtoBuffer(message)
+  if pb.getLengthValue(1, nonce) != -1 and
+     pb.getLengthValue(2, pubkey) != -1 and
+     pb.getLengthValue(3, exchanges) != -1 and
+     pb.getLengthValue(4, ciphers) != -1 and
+     pb.getLengthValue(5, hashes) != -1:
+    result = true
+
 proc createExchange*(epubkey, signature: openarray[byte]): seq[byte] =
+  ## Create SecIO exchange message using ephemeral public key ``epubkey`` and
+  ## signature of proposal blocks ``signature``.
   var msg = initProtoBuffer({WithUint32BeLength})
   msg.write(initProtoField(1, epubkey))
   msg.write(initProtoField(2, signature))
   msg.finish()
   shallowCopy(result, msg.buffer)
 
+proc decodeExchange*(message: seq[byte],
+                     pubkey, signature: var seq[byte]): bool =
+  ## Parse incoming exchange message and decode remote ephemeral public key
+  ## ``pubkey`` and signature ``signature``.
+  ##
+  ## Procedure returns ``true`` on success and ``false`` on error.
+  var pb = initProtoBuffer(message)
+  if pb.getLengthValue(1, pubkey) != -1 and
+     pb.getLengthValue(2, signature) != -1:
+    result = true
+
 ## Serialization/Deserialization helpers
 
 proc write*(vb: var VBuffer, pubkey: PublicKey) {.inline.} =
diff --git a/libp2p/crypto/ecnist.nim b/libp2p/crypto/ecnist.nim
index 81ab34a..7d37c3a 100644
--- a/libp2p/crypto/ecnist.nim
+++ b/libp2p/crypto/ecnist.nim
@@ -141,36 +141,48 @@ template getPublicKeyLength*(curve: EcCurveKind): int =
   of Secp521r1:
     PubKey521Length
 
+template getPrivateKeyLength*(curve: EcCurveKind): int =
+  case curve
+  of Secp256r1:
+    SecKey256Length
+  of Secp384r1:
+    SecKey384Length
+  of Secp521r1:
+    SecKey521Length
+
 proc copy*[T: EcPKI](dst: var T, src: T): bool =
   ## Copy EC `private key`, `public key` or `signature` ``src`` to ``dst``.
   ##
   ## Returns ``true`` on success, ``false`` otherwise.
-  dst = new T
-  when T is EcPrivateKey:
-    let length = src.key.xlen
-    if length > 0 and len(src.buffer) > 0:
-      let offset = getOffset(src)
-      if offset >= 0:
-        dst.buffer = src.buffer
-        dst.key.curve = src.key.curve
-        dst.key.xlen = length
-        dst.key.x = cast[ptr cuchar](addr dst.buffer[offset])
-        result = true
-  elif T is EcPublicKey:
-    let length = src.key.qlen
-    if length > 0 and len(src.buffer) > 0:
-      let offset = getOffset(src)
-      if offset >= 0:
-        dst.buffer = src.buffer
-        dst.key.curve = src.key.curve
-        dst.key.qlen = length
-        dst.key.q = cast[ptr cuchar](addr dst.buffer[offset])
-        result = true
+  if isNil(src):
+    result = false
   else:
-    let length = len(src.buffer)
-    if length > 0:
-      dst.buffer = src.buffer
-      result = true
+    dst = new T
+    when T is EcPrivateKey:
+      let length = src.key.xlen
+      if length > 0 and len(src.buffer) > 0:
+        let offset = getOffset(src)
+        if offset >= 0:
+          dst.buffer = src.buffer
+          dst.key.curve = src.key.curve
+          dst.key.xlen = length
+          dst.key.x = cast[ptr cuchar](addr dst.buffer[offset])
+          result = true
+    elif T is EcPublicKey:
+      let length = src.key.qlen
+      if length > 0 and len(src.buffer) > 0:
+        let offset = getOffset(src)
+        if offset >= 0:
+          dst.buffer = src.buffer
+          dst.key.curve = src.key.curve
+          dst.key.qlen = length
+          dst.key.q = cast[ptr cuchar](addr dst.buffer[offset])
+          result = true
+    else:
+      let length = len(src.buffer)
+      if length > 0:
+        dst.buffer = src.buffer
+        result = true
 
 proc copy*[T: EcPKI](src: T): T {.inline.} =
   ## Returns copy of EC `private key`, `public key` or `signature`
@@ -180,6 +192,7 @@ proc copy*[T: EcPKI](src: T): T {.inline.} =
 
 proc clear*[T: EcPKI|EcKeyPair](pki: var T) =
   ## Wipe and clear EC `private key`, `public key` or `signature` object.
+  doAssert(not isNil(pki))
   when T is EcPrivateKey:
     burnMem(pki.buffer)
     pki.buffer.setLen(0)
@@ -228,6 +241,7 @@ proc random*(t: typedesc[EcPrivateKey], kind: EcCurveKind): EcPrivateKey =
 
 proc getKey*(seckey: EcPrivateKey): EcPublicKey =
   ## Calculate and return EC public key from private key ``seckey``.
+  doAssert(not isNil(seckey))
   var ecimp = brEcGetDefault()
   if seckey.key.curve in EcSupportedCurvesCint:
     var length = getPublicKeyLength(cast[EcCurveKind](seckey.key.curve))
@@ -250,8 +264,9 @@ proc random*(t: typedesc[EcKeyPair], kind: EcCurveKind): EcKeyPair {.inline.} =
 
 proc `$`*(seckey: EcPrivateKey): string =
   ## Return string representation of EC private key.
-  if seckey.key.curve == 0 or seckey.key.xlen == 0 or len(seckey.buffer) == 0:
-    result = "Empty key"
+  if isNil(seckey) or seckey.key.curve == 0 or seckey.key.xlen == 0 or
+     len(seckey.buffer) == 0:
+    result = "Empty or uninitialized ECNIST key"
   else:
     if seckey.key.curve notin EcSupportedCurvesCint:
       result = "Unknown key"
@@ -265,8 +280,9 @@ proc `$`*(seckey: EcPrivateKey): string =
 
 proc `$`*(pubkey: EcPublicKey): string =
   ## Return string representation of EC public key.
-  if pubkey.key.curve == 0 or pubkey.key.qlen == 0 or len(pubkey.buffer) == 0:
-    result = "Empty key"
+  if isNil(pubkey) or pubkey.key.curve == 0 or pubkey.key.qlen == 0 or
+     len(pubkey.buffer) == 0:
+    result = "Empty or uninitialized ECNIST key"
   else:
     if pubkey.key.curve notin EcSupportedCurvesCint:
       result = "Unknown key"
@@ -280,7 +296,45 @@ proc `$`*(pubkey: EcPublicKey): string =
 
 proc `$`*(sig: EcSignature): string =
   ## Return hexadecimal string representation of EC signature.
-  result = toHex(sig.buffer)
+  if isNil(sig) or len(sig.buffer) == 0:
+    result = "Empty or uninitialized ECNIST signature"
+  else:
+    result = toHex(sig.buffer)
+
+proc toRawBytes*(seckey: EcPrivateKey, data: var openarray[byte]): int =
+  ## Serialize EC private key ``seckey`` to raw binary form and store it
+  ## to ``data``.
+  ##
+  ## Returns number of bytes (octets) needed to store EC private key, or `0`
+  ## if private key is not in supported curve.
+  doAssert(not isNil(seckey))
+  if seckey.key.curve in EcSupportedCurvesCint:
+    result = getPrivateKeyLength(cast[EcCurveKind](seckey.key.curve))
+    if len(data) >= result:
+      copyMem(addr data[0], unsafeAddr seckey.buffer[0], result)
+
+proc toRawBytes*(pubkey: EcPublicKey, data: var openarray[byte]): int =
+  ## Serialize EC public key ``pubkey`` to uncompressed form specified in
+  ## section 4.3.6 of ANSI X9.62.
+  ##
+  ## Returns number of bytes (octets) needed to store EC public key, or `0`
+  ## if public key is not in supported curve.
+  doAssert(not isNil(pubkey))
+  if pubkey.key.curve in EcSupportedCurvesCint:
+    result = getPublicKeyLength(cast[EcCurveKind](pubkey.key.curve))
+    if len(data) >= result:
+      copyMem(addr data[0], unsafeAddr pubkey.buffer[0], result)
+
+proc toRawBytes*(sig: EcSignature, data: var openarray[byte]): int =
+  ## Serialize EC signature ``sig`` to raw binary form and store it to ``data``.
+  ##
+  ## Returns number of bytes (octets) needed to store EC signature, or `0`
+  ## if signature is not in supported curve.
+  doAssert(not isNil(sig))
+  result = len(sig.buffer)
+  if len(data) >= len(sig.buffer):
+    if len(sig.buffer) > 0:
+      copyMem(addr data[0], unsafeAddr sig.buffer[0], len(sig.buffer))
 
 proc toBytes*(seckey: EcPrivateKey, data: var openarray[byte]): int =
   ## Serialize EC private key ``seckey`` to ASN.1 DER binary form and store it
@@ -288,6 +342,7 @@ proc toBytes*(seckey: EcPrivateKey, data: var openarray[byte]): int =
   ##
   ## Procedure returns number of bytes (octets) needed to store EC private key,
   ## or `0` if private key is not in supported curve.
+  doAssert(not isNil(seckey))
   if seckey.key.curve in EcSupportedCurvesCint:
     var offset, length: int
     var pubkey = seckey.getKey()
@@ -327,6 +382,7 @@ proc toBytes*(pubkey: EcPublicKey, data: var openarray[byte]): int =
   ##
   ## Procedure returns number of bytes (octets) needed to store EC public key,
   ## or `0` if public key is not in supported curve.
+  doAssert(not isNil(pubkey))
   if pubkey.key.curve in EcSupportedCurvesCint:
     var b = Asn1Buffer.init()
     var p = Asn1Composite.init(Asn1Tag.Sequence)
@@ -357,12 +413,14 @@ proc toBytes*(sig: EcSignature, data: var openarray[byte]): int =
   ##
   ## Procedure returns number of bytes (octets) needed to store EC signature,
   ## or `0` if signature is not in supported curve.
+  doAssert(not isNil(sig))
   result = len(sig.buffer)
   if len(data) >= result:
     copyMem(addr data[0], unsafeAddr sig.buffer[0], result)
 
 proc getBytes*(seckey: EcPrivateKey): seq[byte] =
   ## Serialize EC private key ``seckey`` to ASN.1 DER binary form and return it.
+  doAssert(not isNil(seckey))
   if seckey.key.curve in EcSupportedCurvesCint:
     result = newSeq[byte]()
     let length = seckey.toBytes(result)
@@ -373,6 +431,7 @@ proc getBytes*(seckey: EcPrivateKey): seq[byte] =
 
 proc getBytes*(pubkey: EcPublicKey): seq[byte] =
   ## Serialize EC public key ``pubkey`` to ASN.1 DER binary form and return it.
+  doAssert(not isNil(pubkey))
   if pubkey.key.curve in EcSupportedCurvesCint:
     result = newSeq[byte]()
     let length = pubkey.toBytes(result)
@@ -383,6 +442,37 @@ proc getBytes*(pubkey: EcPublicKey): seq[byte] =
 
 proc getBytes*(sig: EcSignature): seq[byte] =
   ## Serialize EC signature ``sig`` to ASN.1 DER binary form and return it.
+  doAssert(not isNil(sig))
+  result = newSeq[byte]()
+  let length = sig.toBytes(result)
+  result.setLen(length)
+  discard sig.toBytes(result)
+
+proc getRawBytes*(seckey: EcPrivateKey): seq[byte] =
+  ## Serialize EC private key ``seckey`` to raw binary form and return it.
+  doAssert(not isNil(seckey))
+  if seckey.key.curve in EcSupportedCurvesCint:
+    result = newSeq[byte]()
+    let length = seckey.toRawBytes(result)
+    result.setLen(length)
+    discard seckey.toRawBytes(result)
+  else:
+    raise newException(EcKeyIncorrectError, "Incorrect private key")
+
+proc getRawBytes*(pubkey: EcPublicKey): seq[byte] =
+  ## Serialize EC public key ``pubkey`` to raw binary form and return it.
+  doAssert(not isNil(pubkey))
+  if pubkey.key.curve in EcSupportedCurvesCint:
+    result = newSeq[byte]()
+    let length = pubkey.toRawBytes(result)
+    result.setLen(length)
+    discard pubkey.toRawBytes(result)
+  else:
+    raise newException(EcKeyIncorrectError, "Incorrect public key")
+
+proc getRawBytes*(sig: EcSignature): seq[byte] =
+  ## Serialize EC signature ``sig`` to raw binary form and return it.
+  doAssert(not isNil(sig))
   result = newSeq[byte]()
   let length = sig.toBytes(result)
   result.setLen(length)
@@ -390,33 +480,54 @@ proc getBytes*(sig: EcSignature): seq[byte] =
 
 proc `==`*(pubkey1, pubkey2: EcPublicKey): bool =
   ## Returns ``true`` if both keys ``pubkey1`` and ``pubkey2`` are equal.
-  if pubkey1.key.curve != pubkey2.key.curve:
-    return false
-  if pubkey1.key.qlen != pubkey2.key.qlen:
-    return false
-  let op1 = pubkey1.getOffset()
-  let op2 = pubkey2.getOffset()
-  if op1 == -1 or op2 == -1:
-    return false
-  result = equalMem(unsafeAddr pubkey1.buffer[op1],
-                    unsafeAddr pubkey2.buffer[op2], pubkey1.key.qlen)
+  if isNil(pubkey1) and isNil(pubkey2):
+    result = true
+  elif isNil(pubkey1) and (not isNil(pubkey2)):
+    result = false
+  elif isNil(pubkey2) and (not isNil(pubkey1)):
+    result = false
+  else:
+    if pubkey1.key.curve != pubkey2.key.curve:
+      return false
+    if pubkey1.key.qlen != pubkey2.key.qlen:
+      return false
+    let op1 = pubkey1.getOffset()
+    let op2 = pubkey2.getOffset()
+    if op1 == -1 or op2 == -1:
+      return false
+    result = equalMem(unsafeAddr pubkey1.buffer[op1],
+                      unsafeAddr pubkey2.buffer[op2], pubkey1.key.qlen)
 
 proc `==`*(seckey1, seckey2: EcPrivateKey): bool =
   ## Returns ``true`` if both keys ``seckey1`` and ``seckey2`` are equal.
-  if seckey1.key.curve != seckey2.key.curve:
-    return false
-  if seckey1.key.xlen != seckey2.key.xlen:
-    return false
-  let op1 = seckey1.getOffset()
-  let op2 = seckey2.getOffset()
-  if op1 == -1 or op2 == -1:
-    return false
-  result = equalMem(unsafeAddr seckey1.buffer[op1],
-                    unsafeAddr seckey2.buffer[op2], seckey1.key.xlen)
+  if isNil(seckey1) and isNil(seckey2):
+    result = true
+  elif isNil(seckey1) and (not isNil(seckey2)):
+    result = false
+  elif isNil(seckey2) and (not isNil(seckey1)):
+    result = false
+  else:
+    if seckey1.key.curve != seckey2.key.curve:
+      return false
+    if seckey1.key.xlen != seckey2.key.xlen:
+      return false
+    let op1 = seckey1.getOffset()
+    let op2 = seckey2.getOffset()
+    if op1 == -1 or op2 == -1:
+      return false
+    result = equalMem(unsafeAddr seckey1.buffer[op1],
+                      unsafeAddr seckey2.buffer[op2], seckey1.key.xlen)
 
 proc `==`*(sig1, sig2: EcSignature): bool =
   ## Return ``true`` if both signatures ``sig1`` and ``sig2`` are equal.
-  result = (sig1.buffer == sig2.buffer)
+  if isNil(sig1) and isNil(sig2):
+    result = true
+  elif isNil(sig1) and (not isNil(sig2)):
+    result = false
+  elif isNil(sig2) and (not isNil(sig1)):
+    result = false
+  else:
+    result = (sig1.buffer == sig2.buffer)
 
 proc init*(key: var EcPrivateKey, data: openarray[byte]): Asn1Status =
   ## Initialize EC `private key` or `signature` ``key`` from ASN.1 DER binary
@@ -698,6 +809,7 @@ proc scalarMul*(pub: EcPublicKey, sec: EcPrivateKey): EcPublicKey =
   ## Return scalar multiplication of ``pub`` and ``sec``.
   ##
   ## Returns point in curve as ``pub * sec`` or ``nil`` otherwise.
+  doAssert((not isNil(pub)) and (not isNil(sec)))
   var impl = brEcGetDefault()
   if sec.key.curve in EcSupportedCurvesCint:
     if pub.key.curve == sec.key.curve:
@@ -726,6 +838,7 @@ proc toSecret*(pubkey: EcPublicKey, seckey: EcPrivateKey,
   ##
   ## ``data`` array length must be at least 32 bytes for `secp256r1`, 48 bytes
   ## for `secp384r1` and 66 bytes for `secp521r1`.
+  doAssert((not isNil(pubkey)) and (not isNil(seckey)))
   var mult = scalarMul(pubkey, seckey)
   var length = 0
   if not isNil(mult):
@@ -745,6 +858,7 @@ proc getSecret*(pubkey: EcPublicKey, seckey: EcPrivateKey): seq[byte] =
   ## shared secret.
   ##
   ## If error happens length of result array will be ``0``.
+  doAssert((not isNil(pubkey)) and (not isNil(seckey)))
   var data: array[Secret521Length, byte]
   let res = toSecret(pubkey, seckey, data)
   if res > 0:
@@ -754,6 +868,7 @@ proc getSecret*(pubkey: EcPublicKey, seckey: EcPrivateKey): seq[byte] =
 proc sign*[T: byte|char](seckey: EcPrivateKey,
                          message: openarray[T]): EcSignature =
   ## Get ECDSA signature of data ``message`` using private key ``seckey``.
+  doAssert(not isNil(seckey))
   var hc: BrHashCompatContext
   var hash: array[32, byte]
   var impl = brEcGetDefault()
@@ -785,6 +900,7 @@ proc verify*[T: byte|char](sig: EcSignature, message: openarray[T],
   ##
   ## Return ``true`` if message verification succeeded, ``false`` if
   ## verification failed.
+  doAssert((not isNil(sig)) and (not isNil(pubkey)))
   var hc: BrHashCompatContext
   var hash: array[32, byte]
   var impl = brEcGetDefault()
diff --git a/libp2p/crypto/rsa.nim b/libp2p/crypto/rsa.nim
index 0b0ba95..f2205fd 100644
--- a/libp2p/crypto/rsa.nim
+++ b/libp2p/crypto/rsa.nim
@@ -12,7 +12,6 @@
 ## This module uses unmodified parts of code from
 ## BearSSL library <https://bearssl.org/>
 ## Copyright(C) 2018 Thomas Pornin <pornin@bolet.org>.
-
 import nimcrypto/utils
 import common, minasn1
 export Asn1Status
@@ -160,6 +159,7 @@ proc random*[T: RsaKP](t: typedesc[T], bits = DefaultKeySize,
 
 proc copy*[T: RsaPKI](key: T): T =
   ## Create copy of RSA private key, public key or signature.
+  doAssert(not isNil(key))
   when T is RsaPrivateKey:
     if len(key.buffer) > 0:
       let length = key.seck.plen + key.seck.qlen + key.seck.dplen +
@@ -220,6 +220,7 @@ proc copy*[T: RsaPKI](key: T): T =
 
 proc getKey*(key: RsaPrivateKey): RsaPublicKey =
   ## Get RSA public key from RSA private key.
+  doAssert(not isNil(key))
   let length = key.pubk.nlen + key.pubk.elen
   result = new RsaPublicKey
   result.buffer = newSeq[byte](length)
@@ -241,6 +242,7 @@ proc pubkey*(pair: RsaKeyPair): RsaPublicKey {.inline.} =
 
 proc clear*[T: RsaPKI|RsaKeyPair](pki: var T) =
   ## Wipe and clear EC private key, public key or scalar object.
+  doAssert(not isNil(pki))
   when T is RsaPrivateKey:
     burnMem(pki.buffer)
     pki.buffer.setLen(0)
@@ -276,6 +278,7 @@ proc toBytes*(key: RsaPrivateKey, data: var openarray[byte]): int =
   ##
   ## Procedure returns number of bytes (octets) needed to store RSA private key,
   ## or `0` if private key is is incorrect.
+  doAssert(not isNil(key))
   if len(key.buffer) > 0:
     var b = Asn1Buffer.init()
     var p = Asn1Composite.init(Asn1Tag.Sequence)
@@ -308,6 +311,7 @@ proc toBytes*(key: RsaPublicKey, data: var openarray[byte]): int =
   ##
   ## Procedure returns number of bytes (octets) needed to store RSA public key,
   ## or `0` if public key is incorrect.
+  doAssert(not isNil(key))
   if len(key.buffer) > 0:
     var b = Asn1Buffer.init()
     var p = Asn1Composite.init(Asn1Tag.Sequence)
@@ -337,6 +341,7 @@ proc toBytes*(sig: RsaSignature, data: var openarray[byte]): int =
   ##
   ## Procedure returns number of bytes (octets) needed to store RSA public key,
   ## or `0` if public key is incorrect.
+  doAssert(not isNil(sig))
   result = len(sig.buffer)
   if len(data) >= result:
     copyMem(addr data[0], addr sig.buffer[0], result)
@@ -344,6 +349,7 @@ proc toBytes*(sig: RsaSignature, data: var openarray[byte]): int =
 proc getBytes*(key: RsaPrivateKey): seq[byte] =
   ## Serialize RSA private key ``key`` to ASN.1 DER binary form and
   ## return it.
+  doAssert(not isNil(key))
   result = newSeq[byte](4096)
   let length = key.toBytes(result)
   if length > 0:
@@ -354,6 +360,7 @@ proc getBytes*(key: RsaPrivateKey): seq[byte] =
 proc getBytes*(key: RsaPublicKey): seq[byte] =
   ## Serialize RSA public key ``key`` to ASN.1 DER binary form and
   ## return it.
+  doAssert(not isNil(key))
   result = newSeq[byte](4096)
   let length = key.toBytes(result)
   if length > 0:
@@ -363,6 +370,7 @@ proc getBytes*(key: RsaPublicKey): seq[byte] =
 
 proc getBytes*(sig: RsaSignature): seq[byte] =
   ## Serialize RSA signature ``sig`` to raw binary form and return it.
+  doAssert(not isNil(sig))
   result = newSeq[byte](4096)
   let length = sig.toBytes(result)
   if length > 0:
@@ -592,8 +600,8 @@ proc init*[T: RsaPKI](t: typedesc[T], data: string): T {.inline.} =
 
 proc `$`*(key: RsaPrivateKey): string =
   ## Return string representation of RSA private key.
-  if len(key.buffer) == 0:
-    result = "Empty RSA key"
+  if isNil(key) or len(key.buffer) == 0:
+    result = "Empty or uninitialized RSA key"
   else:
     result = "RSA key ("
     result.add($key.seck.nBitlen)
@@ -618,8 +626,8 @@ proc `$`*(key: RsaPrivateKey): string =
 
 proc `$`*(key: RsaPublicKey): string =
   ## Return string representation of RSA public key.
-  if len(key.buffer) == 0:
-    result = "Empty RSA key"
+  if isNil(key) or len(key.buffer) == 0:
+    result = "Empty or uninitialized RSA key"
   else:
     let nbitlen = key.key.nlen shl 3
     result = "RSA key ("
@@ -632,8 +640,8 @@ proc `$`*(key: RsaPublicKey): string =
 
 proc `$`*(sig: RsaSignature): string =
   ## Return string representation of RSA signature.
-  if len(sig.buffer) == 0:
-    result = "Empty RSA signature"
+  if isNil(sig) or len(sig.buffer) == 0:
+    result = "Empty or uninitialized RSA signature"
   else:
     result = "RSA signature ("
     result.add(toHex(sig.buffer))
@@ -656,44 +664,69 @@ proc cmp(a: openarray[byte], b: openarray[byte]): bool =
 
 proc `==`*(a, b: RsaPrivateKey): bool =
   ## Compare two RSA private keys for equality.
-  if a.seck.nBitlen == b.seck.nBitlen:
-    if cast[int](a.seck.nBitlen) > 0:
-      let r1 = cmp(getArray(a.buffer, a.seck.p, a.seck.plen),
-                   getArray(b.buffer, b.seck.p, b.seck.plen))
-      let r2 = cmp(getArray(a.buffer, a.seck.q, a.seck.qlen),
-                   getArray(b.buffer, b.seck.q, b.seck.qlen))
-      let r3 = cmp(getArray(a.buffer, a.seck.dp, a.seck.dplen),
-                   getArray(b.buffer, b.seck.dp, b.seck.dplen))
-      let r4 = cmp(getArray(a.buffer, a.seck.dq, a.seck.dqlen),
-                   getArray(b.buffer, b.seck.dq, b.seck.dqlen))
-      let r5 = cmp(getArray(a.buffer, a.seck.iq, a.seck.iqlen),
-                   getArray(b.buffer, b.seck.iq, b.seck.iqlen))
-      let r6 = cmp(getArray(a.buffer, a.pexp, a.pexplen),
-                   getArray(b.buffer, b.pexp, b.pexplen))
-      let r7 = cmp(getArray(a.buffer, a.pubk.n, a.pubk.nlen),
-                   getArray(b.buffer, b.pubk.n, b.pubk.nlen))
-      let r8 = cmp(getArray(a.buffer, a.pubk.e, a.pubk.elen),
-                   getArray(b.buffer, b.pubk.e, b.pubk.elen))
-      result = r1 and r2 and r3 and r4 and r5 and r6 and r7 and r8
-    else:
-      result = true
+  ##
+  ## Result is true if ``a`` and ``b`` are both ``nil`` or ``a`` and ``b`` are
+  ## equal by value.
+  if isNil(a) and isNil(b):
+    result = true
+  elif isNil(a) and (not isNil(b)):
+    result = false
+  elif isNil(b) and (not isNil(a)):
+    result = false
+  else:
+    if a.seck.nBitlen == b.seck.nBitlen:
+      if cast[int](a.seck.nBitlen) > 0:
+        let r1 = cmp(getArray(a.buffer, a.seck.p, a.seck.plen),
+                     getArray(b.buffer, b.seck.p, b.seck.plen))
+        let r2 = cmp(getArray(a.buffer, a.seck.q, a.seck.qlen),
+                     getArray(b.buffer, b.seck.q, b.seck.qlen))
+        let r3 = cmp(getArray(a.buffer, a.seck.dp, a.seck.dplen),
+                     getArray(b.buffer, b.seck.dp, b.seck.dplen))
+        let r4 = cmp(getArray(a.buffer, a.seck.dq, a.seck.dqlen),
+                     getArray(b.buffer, b.seck.dq, b.seck.dqlen))
+        let r5 = cmp(getArray(a.buffer, a.seck.iq, a.seck.iqlen),
+                     getArray(b.buffer, b.seck.iq, b.seck.iqlen))
+        let r6 = cmp(getArray(a.buffer, a.pexp, a.pexplen),
+                     getArray(b.buffer, b.pexp, b.pexplen))
+        let r7 = cmp(getArray(a.buffer, a.pubk.n, a.pubk.nlen),
+                     getArray(b.buffer, b.pubk.n, b.pubk.nlen))
+        let r8 = cmp(getArray(a.buffer, a.pubk.e, a.pubk.elen),
+                     getArray(b.buffer, b.pubk.e, b.pubk.elen))
+        result = r1 and r2 and r3 and r4 and r5 and r6 and r7 and r8
+      else:
+        result = true
 
 proc `==`*(a, b: RsaSignature): bool =
   ## Compare two RSA signatures for equality.
-  result = (a.buffer == b.buffer)
+  if isNil(a) and isNil(b):
+    result = true
+  elif isNil(a) and (not isNil(b)):
+    result = false
+  elif isNil(b) and (not isNil(a)):
+    result = false
+  else:
+    result = (a.buffer == b.buffer)
 
 proc `==`*(a, b: RsaPublicKey): bool =
   ## Compare two RSA public keys for equality.
-  let r1 = cmp(getArray(a.buffer, a.key.n, a.key.nlen),
-               getArray(b.buffer, b.key.n, b.key.nlen))
-  let r2 = cmp(getArray(a.buffer, a.key.e, a.key.elen),
-               getArray(b.buffer, b.key.e, b.key.elen))
-  result = r1 and r2
+  if isNil(a) and isNil(b):
+    result = true
+  elif isNil(a) and (not isNil(b)):
+    result = false
+  elif isNil(b) and (not isNil(a)):
+    result = false
+  else:
+    let r1 = cmp(getArray(a.buffer, a.key.n, a.key.nlen),
+                 getArray(b.buffer, b.key.n, b.key.nlen))
+    let r2 = cmp(getArray(a.buffer, a.key.e, a.key.elen),
+                 getArray(b.buffer, b.key.e, b.key.elen))
+    result = r1 and r2
 
 proc sign*[T: byte|char](key: RsaPrivateKey,
                          message: openarray[T]): RsaSignature =
   ## Get RSA PKCS1.5 signature of data ``message`` using SHA256 and private
   ## key ``key``.
+  doAssert(not isNil(key))
   var hc: BrHashCompatContext
   var hash: array[32, byte]
   var impl = BrRsaPkcs1SignGetDefault()
@@ -720,6 +753,7 @@ proc verify*[T: byte|char](sig: RsaSignature, message: openarray[T],
   ##
   ## Return ``true`` if message verification succeeded, ``false`` if
   ## verification failed.
+  doAssert((not isNil(sig)) and (not isNil(pubkey)))
   if len(sig.buffer) > 0:
     var hc: BrHashCompatContext
     var hash: array[32, byte]
diff --git a/tests/testcrypto.nim b/tests/testcrypto.nim
index 5f13a90..be2d047 100644
--- a/tests/testcrypto.nim
+++ b/tests/testcrypto.nim
@@ -345,7 +345,7 @@ const
 proc cmp(a, b: openarray[byte]): bool =
   result = (@a == @b)
 
-proc testStretcher(s, e: int, cs: CipherScheme, ds: DigestSheme): bool =
+proc testStretcher(s, e: int, cs: string, ds: string): bool =
   for i in s..<e:
     var sharedsecret = fromHex(stripSpaces(Secrets[i]))
     var secret = stretchKeys(cs, ds, sharedsecret)
@@ -452,8 +452,8 @@ suite "Key interface test suite":
         recsig2.verify(bmsg, recpub2) == true
 
   test "Go key stretch function AES128-SHA256 test vectors":
-    check testStretcher(0, 4, Aes128, Sha256) == true
+    check testStretcher(0, 4, "AES-128", "SHA256") == true
   test "Go key stretch function AES256-SHA512 test vectors":
-    check testStretcher(4, 8, Aes256, Sha512) == true
+    check testStretcher(4, 8, "AES-256", "SHA512") == true
   test "Go key stretch function AES256-SHA1 test vectors":
-    check testStretcher(8, 12, Aes256, Sha1) == true
+    check testStretcher(8, 12, "AES-256", "SHA1") == true