diff --git a/protocol/zcash.bib b/protocol/zcash.bib
index e4447f16..437773b1 100644
--- a/protocol/zcash.bib
+++ b/protocol/zcash.bib
@@ -2,8 +2,10 @@
    presort={BCGGMTV2014},
    author={Eli Ben-Sasson and Alessandro Chiesa and Christina Garman and Matthew Green and Ian Miers and Eran Tromer and Madars Virza},
    title={Zerocash: Decentralized {A}nonymous {P}ayments from {B}itcoin (extended version)},
-   url={http://zerocash-project.org/media/pdf/zerocash-extended-20140518.pdf},
-   urldate={2016-08-06},
+   url={https://eprint.iacr.org/2014/349},
+   urldate={2021-04-05},
+   howpublished={Cryptology ePrint Archive: Report 2014/349.
+Received May~19, 2014.},
    addendum={A condensed version appeared in \textsl{Proceedings of the IEEE Symposium on Security and Privacy (Oakland) 2014},
 pages 459--474; IEEE, 2014.}
 }
@@ -271,8 +273,8 @@ Last revised October~27, 2016.}
 (Dallas, TX, USA, November~3, 2017); post-workshop of the 2017 ACM SIGSAC
 Conference on Computer and Communications Security},
    publisher={ACM},
-   url={http://sci-hub.tw/10.1145/3140649.3140652},
-   urldate={2019-01-09}
+   url={https://sci-hub.tf/10.1145/3140649.3140652},
+   urldate={2021-04-05}
 }
 
 @phdthesis{Hisil2010,
@@ -294,8 +296,8 @@ Proceedings of the 9th International Conference on Theory and Practice in Public
 (New York, NY, USA, April~24--26, 2006)},
    publisher={Springer-Verlag},
    date={2006-02-09},
-   url={http://cr.yp.to/papers.html#curve25519},
-   urldate={2016-08-14},
+   url={https://cr.yp.to/papers.html#curve25519},
+   urldate={2021-04-05},
    addendum={Document ID: 4230efdfa673480fc079449d90f322c0.}
 }
 
@@ -307,8 +309,8 @@ Proceedings of the 9th International Conference on Theory and Practice in Public
    volume={2},
    pages={77--89},
    date={2011-09-26},
-   url={http://cr.yp.to/papers.html#ed25519},
-   urldate={2016-08-14},
+   url={https://cr.yp.to/papers.html#ed25519},
+   urldate={2021-04-05},
    addendum={Document ID: a1a62a2f76d23f65d622484ddd09caf8.}
 }
 
@@ -431,10 +433,10 @@ Received March~20, 2012.}
    presort={Unicode},
    author={The Unicode Consortium},
    publisher={The Unicode Consortium},
-   year={2016},
+   year={2020},
    title={The Unicode Standard},
-   url={http://www.unicode.org/versions/latest/},
-   urldate={2016-08-31}
+   url={https://www.unicode.org/versions/latest/},
+   urldate={2021-04-05}
 }
 
 @misc{libsodium,
@@ -477,8 +479,8 @@ Received March~20, 2012.}
    presort={RIPEMD160},
    author={Hans Dobbertin and Antoon Bosselaers and Bart Preneel},
    title={{RIPEMD}-160, a strengthened version of {RIPEMD}},
-   url={http://homes.esat.kuleuven.be/~bosselae/ripemd160.html},
-   urldate={2016-09-24}
+   url={https://homes.esat.kuleuven.be/~bosselae/ripemd160.html},
+   urldate={2021-04-05}
 }
 
 @misc{ANWW2013,
@@ -806,8 +808,8 @@ Proceedings of the 30th Annual International Cryptology Conference
    title={Standards for {E}fficient {C}ryptography 2 ({SEC} 2)},
    date={2010-01-27},
    addendum={Version 2.0.},
-   url={http://www.secg.org/sec2-v2.pdf},
-   urldate={2016-08-14}
+   url={https://www.secg.org/sec2-v2.pdf},
+   urldate={2021-04-05}
 }
 
 @inproceedings{MAEA2010,
@@ -896,8 +898,8 @@ Last revised February~5, 2018.}
    author={Tom Elvis Jedusor},
    title={Mimblewimble},
    note={July~19, 2016},
-   url={http://diyhpl.us/~bryan/papers2/bitcoin/mimblewimble.txt},
-   urldate={2018-04-03}
+   url={https://diyhpl.us/~bryan/papers2/bitcoin/mimblewimble.txt},
+   urldate={2021-04-05}
 }
 
 @misc{Dalek-notes,
@@ -1474,8 +1476,8 @@ Last revised February~5, 2018.}
    publisher={IEEE},
    date={2000-08-29},
    title={IEEE {S}td 1363-2000: {S}tandard {S}pecifications for {P}ublic-{K}ey {C}ryptography},
-   url={http://ieeexplore.ieee.org/servlet/opac?punumber=7168},
-   urldate={2016-08-03},
+   url={https://ieeexplore.ieee.org/document/891000},
+   urldate={2021-04-05},
    doi={10.1109/IEEESTD.2000.92292}
 }
 
@@ -1486,8 +1488,8 @@ Last revised February~5, 2018.}
    date={2004-09-02},
    title={IEEE {S}td 1363a-2004: {S}tandard {S}pecifications for {P}ublic-{K}ey {C}ryptography --
 {A}mendment 1: {A}dditional {T}echniques},
-   url={http://ieeexplore.ieee.org/servlet/opac?punumber=9276},
-   urldate={2016-08-03},
+   url={https://ieeexplore.ieee.org/document/1335427},
+   urldate={2021-04-05},
    doi={10.1109/IEEESTD.2004.94612}
 }
 
@@ -1770,8 +1772,8 @@ Proceedings of the 14th Annual International Cryptology Conference
    date={1991-02},
    publisher={Universität Karlsruhe Fakultät für Informatik},
 %   doi={10.1.1.34.8570},
-   url={http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.34.8570},
-   urldate={2018-02-17},
+   url={https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.34.8570},
+   urldate={2021-04-05},
    addendum={An extended abstract appeared in
 \textsl{Advances in Cryptology - CRYPTO~'91:
 Proceedings of the 11th Annual International Cryptology Conference